'Ifaimner   School  Of   Chemistry 


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UNIVERSITY  OF  CALIFORNIA 


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Accession  N o.(0j /j~/X .       Class  No.. 


THE    NEW 


TEXT-BOOK  OF  CHEMISTRY 


FOR  USE  IN 


HIGH    SCHOOLS    AND    ACADEMIES 


BY 

LE  ROY  c.  COOLEY,  PH.  D. 

PBOPESSO  •   OP  PHYSICS  AND  CHEMISTRY  IN  VASSAR  COLLEGE 


IVISON,   BLAKEMAN  &   COMPANY, 

PUBLISHERS, 
NEW  YORK  AND  CHICAGO. 


(0357  f 

COPYRIGHT,  18«9. 


COPYRIGHT,  1881, 
BY  LE  ROY  C.  COOLEY. 


PBEFACE. 


THE  sole  purpose  of  this  volume  is  to  provide  an  ele- 
mentary course  of  chemistry  suited  to  the  wants  of  students 
and  teachers  in  high  schools  and  academies. 

With  this  purpose  in  view  I  have  endeavored,  — 

I.  To  seize  upon  the  fundamental  facts  and  principles  of 
the  science,  and  submit  them  to  a  simple  and  concise,  but  at 
the  same  time  a  clear  and  accurate,  treatment. 

II.  To  present  the  subjects  which  will  be  of  greatest  value 
to  a  student  whose  course  of  study  must  end  when  he  leaves 
the   preparatory  school,  and  which   are,  at  the  same  time, 
most  desirable,  as  a  preparation  for  higher  courses,  to  those 
who  may  in  future  pursue  them. 

III.  To  thoroughly  systematize  the  whole,  securing  a  logi- 
cal order  of  subjects  and  an  arrangement  of  topics  adapted 
to  encourage  the  best  methods  of  study  and  to  facilitate  the 
best  methods  of  teaching. 

IV.  To  encourage  a  complete  mastery  of  what  is  under- 
taken, by  concentrating  study  upon  a  brief  course,  and  pro- 
viding for  thorough  reviews  at  short  intervals  by  means  of 
summaries  of  principles  and  exercises  with  problems  at  the 
ends  of  sections  or  chapters. 

V.  To  present  the  science  in  the  light  of  modern  theories, 
sparing  no  pains  to  make  the  work  represent  the  present  state 
of  chemistry  fairly  and  fully,  so  far  as  its  elementary  char- 
acter will  permit. 

iii 


IV  PREFACE. 

VI.  To  make  the  experimental  method  of  reaching  facts 
prominent  and  practicable,  not  by  requiring  the  student  to 
read  the  descriptions  of  large  numbers  of  experiments  which 
he  can  not  make  and  may  never  see,  but  rather  by  inviting 
his  attention  to  a  few  which  are  within  reach,  or  which  may 
be  clearly  understood  by  means  of  cuts,  and  then  providing 
an  additional  number  which  are  easily  and  cheaply  made,  and 
which  are  to  be  studied  only  when  they  are  seen. 

Chemistry  is  eminently  an  experimental  science.  Noth- 
ing whatever  can  be  learned  in  it  by  speculation,  and  very 
little  by  direct  observation  of  nature.  All  its  laws  and 
principles  have  been  established  by  experiment.  The  experi- 
mental method  is  therefore  the  method  of  study  which  is 
true  to  the  character  of  this  subject,  and  it  should  be  promi- 
nent in  an  elementary  course. 

Nevertheless  it  is  not  thought  that  a  student  should  be 
compelled  to  learn  every  thing  in  chemistry  by  the  study  of 
experiments.  He  will  acquire  a  larger  knowledge  and  a 
good  discipline  if  he  take  many  established  facts  and  laws 
without  witnessing  the  experimental  evidence  on  which  they 
rest.  And,  indeed,  this  he  must  do,  or  accomplish  little,  so 
long  as  chemistry  is  compressed  into  the  small  space  which 
it  usually  occupies  in  our  schools.  But  while  so  much  of  the 
world's  progress  in  art,  in  industry,  and  also  in  those  beliefs 
which  sway  the  minds  and  characters  of  men,  is  based  upon 
the  experimental  method  of  reaching  the  facts  and  laws  of 
nature,  chemistry,  above  all  other  sciences,  should  take  to 
itself  the  privilege  and  the  duty  of  teaching  the  young  to 
know  what  an  experiment  really  is,  how  to  translate  it,  how 
to  weigh  its  testimony,  and  how,  by  means  of  this  method, 
facts  may  be  revealed  and  laws  established. 

These  considerations  have  prompted  me  to  furnish  two 
sets  of  experiments.  I  have  in  the  first  place  illustrated  the 
text  by  experiments,  the  study  of  which  constitutes  a  part  of 
the  student's  daily  preparation.  These  experiments  should 
be  witnessed  if  possible,  but  will,  in  any  case,  impress  the 


PREFACE.  V 

fact  that  the  principles  of  chemistry  rest  on  experiment  for 
their  demonstration.  In  the  second  place,  I  have  provided, 
for  the  teacher's  use,  a  selection  of  additional  experiments, 
easy,  cheap,  and  appropriate  for  illustration,  which  may  be 
used  at  discretion,  and  which,  having  the  charm  of  novelty 
to  the  student,  will  more  effectually  fix  his  attention,  and 
arouse  his  thoughts. 

LER.  C.  C. 
JUNE,  1881. 


CONTENTS. 


CHAPTER  I. 

GENERAL   PRINCIPLES   OF   THE   SCIENCE. 

SECTION  PAGE 

I.  PHYSICAL  AND  CHEMICAL  CHANGES     ....  1 

II.  CHEMICAL  ATTRACTION 10 

III.  INDESTRUCTIBILITY  OF  MATTER 17 

IV.  ANALYSIS  AND  SYNTHESIS 23 

Y.  THE  LAWS  OF  COMBINATION 29 

VI.   CHEMICAL  SYMBOLS  AND  FORMULAS  39 


CHAPTER  II. 

THE   NON-METALLIC    ELEMENTS. 

SECTION  PAGE 

I.   GENERAL  DESCRIPTION 52 

II.  HYDROGEN 60 

III.  THE  UNIVALENT  NON-METALS 70 

IV.  THE  BIVALENT  NON-METALS 83 

V.  THE  TRIVALENT  NON-METALS 115 

VI.  THE  QUADRIVALENT  NON-METALS       ....  143 

VII.  COMBUSTION 159 

vii 


yiii  CONTENTS. 

CHAPTER  III. 

THE   COMPOUNDS   OF   CARBON. 

SECTION  PAGE 

I.  GENERAL,  STATEMENTS 180 

II.  MARSH-GAS  AND  THE  MARSH-GAS  SERIES  .        .        .  182 

III.  THE  ALCOHOLS 186 

IV.  THE  ETHERS     .        .  _  . 189 

V.   OLEFIANT  GAS  AND  THE  OLEFINES    ....  191 

VI.  DESTRUCTIVE  DISTILLATION 192 

VII.  THE  SUGARS 203 

.....          -: 

CHAPTER  IV. 

THE   METALS. 

SECTION  PAGE 

I.  GENERAL  DESCRIPTION  .        .        .       .        .       .        .  214 

II.  METALS  OF  THE  ALKALIES    .       .        .        .        .        .  216 

.  III.  METALS  OF  THE  ALKALINE  EARTHS    .       .        .        .  219 

IV.  METALS  OF  THE  EARTHS 221 

V.  METALS  OF  THE  ZINC  CLASS 223 

VI.   METALS  OF  THE  IRON  CLASS 224 

VII.  METALS  OF  THE  TIN  CLASS  ...... 230 

VIII.   METALS  OF  THE  ANTIMONY  CLASS       ....  230 

_  IX.  METALS  OF  THE  LEAD  CLASS       .....  232 

X.  METALS  OF  THE  SILVER  CLASS     .        .        .        .        .  233 

XL   METALS  OF  THE  GOLD  CLASS       .        .        .        .        .  242 

APPENDIX. 

EASY  EXPERIMENTS. FOR. THE.  CLASS-ROOM                     .        .  251 


CHAPTER  I. 
GENERAL  PRINCIPLES  OF  THE  SCIENCE. 


SECTION   I. 

PHYSICAL  AND  CHEMICAL  CHANGES. 

1.  Physical  Changes.  —  Bodies  of  matter  are  constantly 
changing.    They  move  :  how  varied  are  their  motions  !    They 
change  their  shapes,  as  when  rocks  are  rounded  by  the  flow 
of  water  over  them,  or  shattered  by  a  blast  of  gunpowder. 
They  change  from  solid  to  liquid  forms,  as  when  the  snows 
of  winter  melt ;  and  from  liquids  to  gases,  as  when  water 
passes   into   steam.      In   such   changes   as  these,  however, 
the  nature  of  the  substance  is  not  affected.     After  a  body 
has  moved,  it  is  the  same  body  as  before.     Water,  in  the 
forms  of  ice  and  dew  and  vapor,  is  water ;  and,  if  it  change 
from   one   to   another,  it  is  water  still.     Such  changes  are 
called  PHYSICAL  CHANGES.     They  are  changes  during  which 
the  nature  of  a  substance  remains  unaltered. 

2.  Illustrated  by  Experiment.  —  A    simple   experiment 
with  an  apparatus  shown  in  Fig.   1  will  show  that  air  will 
yield  to  the  slightest  pressure,  and  suffer  a  change  in  its  vol- 
ume and  in  its  density. 

1 


2  CHEMISTRY. 

A  glass  tube  with  a  bulb  at  the  upper  end  is  joined  to  an- 
other by  a  piece  of  rubber  tubing.     A  colored  liquid  fills  the 
rubber,  and  stands  at  equal  heights  in  the  glass  tubes.     The 
bulb  and  stem  above  the  liquid  are  filled  with  air. 
Let  the  lips  be  applied  now  to  the  top  of  the  open 
tube,'  and  the  breath  be  gently  forced  into  it :  the 
fluid   quickly  responds  to  the  pressure,  and  rises 
towards  the  bulb,  pushing  the  air  before  it  into  a 
smaller  space.     The  volume  of   the  air  is  dimin- 
ished, and  its  density  is  increased. 

But  the  nature  of  the  substance  is  not  altered. 
The  same  air  remains,  after  the  pressure  is  exerted, 
as  before.  These  changes  in  volume  and  density 
are  examples  of  physical  changes. 

3.  Chemical  Changes.  —  But  all  changes  are 
not  like  these.  Wood  burns  :  in  doing  so  it  ceases 
to  be  wood ;  it  is  changed  to  smoke  and  ash. 
Gunpowder  explodes :  it  is  no  longer  gunpowder. 
Fluids  from  the  soil,  and  gases  from  the  air,  are 
taken  into  the  roots  and  leaves  of  plants,  and  are 
there  changed  into  substances  which  form  the  plant 
itself.  Such  as  these  are  changes  in  the  nature  of  sub- 
stances. They  are  called  CHEMICAL  CHANGES.  They  are 
changes  in  which  we  discover  the  production  of  new  sub- 
stances, substances  totally  unlike  those  which  enter  into  the 
action. 

4.  Illustrated  by  Experiment.  —  A  piece  of  cardboard 
is  put  over  the  top  of  an  ale-glass  (Fig.  2).  A  teaspoonful 
of  sugar  and  another  of  potassium  chlorate  are  powdered  and 
mixed,  and  then  laid  upon  the  cardboard.  Three  or  four 
drops  of  strong  sulphuric  acid  are  allowed  to  fall  from  the  end 
of  a  glass  tube  upon  this  mixture.  Almost  upon  the  instant 
when  the  acid  touches  the  powder,  violet-colored  tongues  of 
flame  leap  up  from  it  with  a  hissing  sound,  accompanied 
with  large  volumes  of  white  vapor  passing  off  into  the 


CHEMISTRY. 


3 


air.  When  the  sound  has  ceased,  and  the  colored  flames 
have  died  out,  only  a  coal-black  mass  is  left  upon  the  card- 
board. 

The  white  mixture  of  sugar  and  potassium  chlorate,  with 
the  drops  of  oily-looking  acid,  have  been 
changed  into  vapors,  which  have  gone  into 
the  air,  and  a  black  coaly  mass,  which  is  left 
behind.  Not  a  particle  of  either  of  the  sub- 
stances used  can  be  found  remaining. 

Burning  of  Sulphur  in  Oxygen.  —  An- 
other illustration  is  seen  in  the  action  of 
oxygen  gas  and  ignited  sulphur.  A  large 
bottle  is  filled  with  oxygen.  A  small  pendant 
spoon  is  fixed  to  the  cork,  and  filled  with 
powdered  sulphur.  The  sulphur,  first  set  on 
fire,  is  thrust  into  the  bottle  (Fig.  3),  when 
the  combustion  goes  on  with  a  fine  blue 
flame,  and  the  bottle  is  soon  filled  with  whitish  vapors. 

The  sulphur  has  now  disappeared.    Much  of  the  oxygen  has 
been  also  used  up.    The  new  gas  formed  contains  them  both, 

but  its  properties  are  not  like 
those  of  either.  It  is  very 
suffocating  when  breathed : 
oxygen  is  not.  Pour  a  little 
solution  of  blue  litmus  into  the 
bottle  :  it  is  first  reddened  and 
then  bleached.  Neither  oxy- 
gen nor  sulphur  can  bleach 
blue  litmus.  The  mutual  ac- 
tion of  the  sulphur  and  oxygen 
is  called  a  CHEMICAL  ACTION, 
because  it  has  brought  about 


Fig.  3. 


a  change  in  the  nature  of  these 
substances,    producing   a  new 

kind  of   matter  having   properties   different   from  those  of 

either  sulphur  or  oxygen. 


4  CHEMISTRY. 

5.  Chemical  Combination.  —  In  this  chemical  action  of 
sulphur  and  oxygen,  we  find  two  substances  uniting  to  form  a 
third.  This  is  a  case  of  chemical  combination. 

In  the  following  experiment  (Fig.  4),  we  may  see  another 
example  of  the  same  kind  of  action.  A  small  quantity  of 
pure  mercury  is  put  into  a  glass  flask  over  a  source  of  heat. 
A  bent  glass  tube  reaches  from  the  flask  over  into  a  vessel  of 
mercury.  The  flask  and  tube  are  filled  with  oxygen.  The 
end  of  the  tube  is  bent  upward  ;  and  over  it  is  placed  a  glass 


Fig.  4. 

jar,  mouth  downward,  also  filled  with  oxygen.  Mercury  and 
oxygen  are  the  only  two  substances  in  the  flask.  If  the 
mercury  be  heated  for  several  hours,  without  boiling,  two 
things  will  be  discovered  :  yellowish  or  red  scales  make  their 
appearance  upon  the  surface  of  the  mercury  in  the  flask,  in- 
creasing in  quantity  until,  if  the  heat  be  continued,  the  metal 
is  completely  covered.  At  the  same  time  the  mercury  rises 
in  the  jar  which  contains  the  oxygen,  showing  that  a  part  of 
that  gas  has  been  removed. 

Some  of  the  mercury  and  some  of  the  oxygen  have  united 
to   produce   this   new  red   substance.      Their  action  is   an 


CHEMISTRY.  5 

example  of  chemical  combination,  since  the  product  contains 
them  both,  and  is  a  substance  quite  unlike  either. 

6.  Chemical  Decomposition.  —  If  the  red  powder,  which 
contains  mercury  and  oxygen,  and  which  the  chemist  calls 
mercuric  oxide,  is  heated,  both  the  mercury  and  the  oxygen 
can  be  regained. 

For  this  purpose  a  tube  (Fig.  5)  containing  a  small 
quantity  of  the  oxide  is  tightly  closed  with  a  perforated 
cork,  from  which  a  bent  tube  passes  just  through  the  cork  of 
a  glass  flask  full  of  water.  Another  bent  tube,  through  this 
same  cork,  reaches  to  the  bottom  of  the  water,  while  its  other 
end  passes  into  the  neck 
of  a  second  flask.  By 
heating  the  tube,  first 
the  red  oxide  becomes 
black,  and  soon  after  a 
colorless  gas  will  push 
the  water  over  into  the 
second  flask. 

Little  globules  of  shining  mercury  will  be  found  clinging 
to  the  sides  of  the  tube  ;  while,  if  the  cork  and  tubes  be 
removed  from  the  first  flask  and  a  lighted  taper  be  plunged 
into  it,  the  flame  will  burst  into  brilliant  combustion,  showing 
the  gas  to  be  oxygen. 

Here  we  find  a  single  substance  broken  into  two  quite  dif- 
ferent ones.  This  is  an  example  of  chemical  decomposition. 

Of  Water.  —  The  decomposition  of  water  is  another  ex- 
ample of  this  kind  of  chemical  action.  It  is  done  by  means 
of  electricity  in  an  apparatus  shown  in  Fig.  6. 

Two  tall  glass  tubes  are  first  filled  with  acidulated  water, 
and  then  inverted  over  two  strips  of  platinum  at  the  bottom 
of  a  vessel  containing  the  same  liquid.  These  pieces  of 
platinum  may  be  joined  by  wires  to  the  poles  of  a  galvanic 
battery.  The  moment  such  a  connection  is  made,  bubbles  of 
gas  begin  to  rise  from  each  platinum,  and  are  collected  in  the 


6 


CHEMISTRY. 


tubes  above.  After  a  little  time  the  tubes  will  be  full  of  the 
colorless  gases  into  which  the  water  has  been  converted. 

If  then  one  tube  be  lifted  from  the  water,  a  lighted  taper 
may  be  thrust  into  it,  when  the  flame  will  instantly  burst  into 
tenfold  brilliancy,  showing  that  the  gas  is  oxygen.  But  if 
the  other  tube  be  lifted,  and  the  flame  applied,  the  gas 
instantly  takes  fire,  and  burns  with  a  slight  explosion.  This 
is  characteristic  of  hydrogen. 

The  electricity  has  produced  a  chemical  decomposition  of 
the  water :  it  has  changed  it  into  oxygen  and  hydrogen,  two 





Fig.  6. 


substances  altogether  different  from  that  from  which  they 
were  derived. 

7.  Definition  of  Chemistry.  —  Chemistry  is  the  science 
which  describes  the  chemical  changes  which  occur  in  bodies 
of  matter,  discovers  the  circumstances  under  which  they  take 
place,  and  the  laws  by  which  they  are  governed. 

8.  Observation  and  Experiment.  —  Many  things  can 
be  learned  by  simply  watching  what  occurs  in  the  ordinary 
operations  of  nature.     The  rusting  of  iron,  for  example,  is 
a  very  common  occurrence.     All  have  seen  the  bright  metal, 


CHEMISTRY.  7 

on  exposure  to  moist  air,  become  covered  with  a  dull  red 
coating ;  and,  since  iron-rust  is  a  substance  totally  different 
from  either  iron  or  moist  air,  we  may  say  that  these  two 
substances,  on  contact,  enter  into  a  chemical  action.  This 
method  of  learning  the  truths  of  nature  is  called  OBSERVA- 
TION. 

But  it  is  likely  that  we  should  never  have  learned  by 
observation  that  water  is  composed  of  two  invisible  gases, 
because  its  decomposition  does  not  happen  in  nature  under 
circumstances  in  which  we  are  able  to  observe  it.  It  was 
discovered  by  means  of  an  experiment.  An  experiment  is 
an  operation  performed  under  conditions  tvhich  we  ourselves 
arrange  for  the  purpose.  Nicholson  and  Carlisle,  in  the 
year  1800,  placed  the  poles  of  their  galvanic  battery  in  a 
vessel  of  water,  and  in  this  way  brought  electricity  to  act 
upon  that  liquid  in  a  manner  not  to  be  seen  in  nature  ;  and 
the  result  was  the  decomposition  of  the  water  into  oxygen 
and  hydrogen.  This  method  of  learning  the  truths  of  nature 
is  called  the  EXPERIMENTAL  METHOD. 

Chemistry  is  an  experimental  science.  Very  little  oi 
what  it  teaches  has  been  discovered  by  observation.  Nearly 
every  thing  we  know  of  chemistry  has  been  established  by 
experiment ;  and  the  student  should  pursue  the  study  of  it 
by  the  experimental  method. 

An  experiment  in  chemistry  is  of  no  value  except  as  it 
teaches  some  chemical  truth.  However  attractive  it  may  be, 
or  however  startling,  if  it  had  no  other  merit  than  beauty 
or  novelty,  it  is  worthless  to  the  student  of  chemistry. 

In  order  to  learn  by  an  experiment,  one  must  see  clearly 
the  conditions  under  which  the  substances  are  brought 
together,  observe  accurately  the  changes  which  occur,  and 
the  products  of  them  ;  and,  finally,  he  must  endeavor  to  see 
that  the  fact  or  principle,  which  the  experiment  claims  to 
prove,  is  a  correct  interpretation  of  the  results. 


CHEMISTRY. 


REVIEW. 

I.  -  SUMMARY   OF  PRINCIPLES. 

9.  Physical  changes  are  such  as  do  not  affect  the  nature 
of  a  substance.  They  are  the  result  of  mechanical  action. 

Chemical  changes  are  such  as  cause  an  alteration  in  the 
nature  of  a  substance,  converting  it  into  a  different  kind  of 
matter.  They  are  the  result  of  chemical  action. 

Chemistry  is  the  science  which  treats  of  the  chemical 
changes  in  all  kinds  of  matter,  discovers  the  conditions  under 
which  they  occur,  the  laws  which  govern  them,  and  describes 
the  qualities  of  substances  which  take  part  in  them,  or  are 
produced  by  them. 

Chemical  combination  is  the  uniting  of  two  or  more  sub- 
stances to  form  a  single  one  with  entirely  different  prop- 
erties. 

When  sulphur  burns  in  oxygen,  these  two  substances  unite 
to  form  sulphurous  oxide,  a  suffocating  gas  quite  unlike 
either  sulphur  or  oxygen.  When  mercury  is  heated  in 
oxygen,  these  two  unite  to  form  mercuric  oxide,  which  resem- 
bles neither  of  them.  These  are  examples  of  chemical 
combination. 

Chemical  decomposition  is  the  breaking-up  of  a  single 
substance  into  two  or  more  simpler  ones,  with  entirely  dif- 
ferent properties. 

Mercuric  oxide,  when  strongly  heated,  is  changed  into 
mercury  and  oxygen.  Water  is  broken,  by  the  electric  cur- 
rent, into  oxygen  and  hydrogen  gases.  These  are  examples 
of  chemical  decomposition. 

Neither  oxygen,  nor  hydrogen,  nor  sulphur,  nor  mercury, 
can  be  decomposed  by  any  known  process.  On  this  account 
they  are  called  ELEMENTS. 

An  element  is  a  substance  which  has  never  yet  been 
decomposed. 

When  two  or  more  substances  enter  into  chemical  com- 
bination, the  new  substance  formed  is  called  a  COMPOUND. 


CHEMISTRY.  9 

A  compound  is  a  substance  made  up  of  two  or  more  sim- 
pler ones,  and  whose  properties  are  unlike  those  of  either 
of  them. 

Besides  elements  and  compounds,  there  are  substances 
called  MIXTURES. 

A  mixture  is  a  substance  made  up  of  two  or  more  which 
have  not  combined.  Its  properties  are  the  same  as  the  prop- 
erties of  its  constituents. 

II.  —  EXERCISES. 

How  many  kinds  of  changes  occur  in  bodies? 

Give  examples  of  physical  changes.  Why  are  these  called 
physical  changes  ? 

Give  example  of  chemical  changes.  Why  are  these  called 
chemical  changes?  Salt  dissolves  in  water:  is  the  change 
physical,  or  chemical?  Iron  rusts:  is  this  a  physical,  or  a 
chemical  change?  The  loftiest  tree  may  be  shattered  into 
fragments  by  a  lightning-stroke:  which  kind  of  change  is 
produced  9 

Define  chemistry. 

What  phenomena  are  to  be  studied  in  chemistry?  In 
natural  philosophy?  Which  science  explains  the  fall  of  a 
stone  ?  the  decay  of  wood  ?  the  manufacture  of  glass  out  of 
potash  and  sand? 

What  is  meant  by  chemical  combination  ? 

What  is  meant  by  chemical  decomposition  ? 

What  is  the  experimental  method  ? 

What  is  the  method  of  observation  ? 

What  is  an  element?    A  compound?    A  mixture? 

What  is  produced  by  burning  sulphur  in  oxygen?  By 
heating  mercury  a  long  time  in  air?  Why  are  these  new 
substances  called  compounds? 

What  are  the  elements  in  water? 

How  may  water  be  decomposed9 


10  CHEMISTBY. 


SECTION  II. 

CHEMICAL  ATTRACTION. 

10.  Attraction.  —  If  we  suspend  a  long  and  light  wooden 
bar  by  means  of  a  thread  attached  to  its  middle  point,  or 
balance  it  on  a  pivot,  and  if  then  we  briskly  rub  a  glass  tube 
with  a  piece  of  silk  or  flannel,  we  shall  find  that  the  end  of 

the  bar  will  swing 
toward  the  glass, 
even  when  the 
glass  is  several 
inches  away  from 
it.  (Fig.  7.)  In 
this  experiment 
we  see  the  action 
of  a  force  which 
tends  to  bring 
these  two  bodies 
together.  Any 

force  by  which  bodies  tend  to  approach  is  called  ATTRACTION. 
Varieties  of  Attraction.  —  We  know  that  all  bodies,  if 
not  supported,  will  fall  to  the  ground :  this  we  learn  by 
observation.  Experiments  have  been  made  which  show  that 
there  is  also  an  attraction  between  bodies  of  every  size  and 
kind.  This  attraction  which  acts  between  all  separate 
bodies,  and  throughout  all  distances  however  great,  is  called 
GRAVITATION. 

Again,  we  know  that  the  parts  of  a  solid  body  are  not  to 
be  separated  with  perfect  ease ;  and  the  attraction  which 
holds  the  particles  of  a  body  together  is  called  COHESION. 

Neither  gravitation  nor  cohesion  produces  any  chemical 
changes  whatever.  But  we  have  seen  that  when  sulphur  and 
oxygen  are  heated,  they  fall  together  into  such  intimate  con- 
tact, that  neither  sulphur  nor  oxygen  can  be  distinguished, 
but  sulphurous  oxide  is  found  instead.  The  attraction  which 


CHEMISTRY.  11 

brings  these  two  elements  into  chemical  combination  is  called 
CHEMICAL  ATTRACTION. 

The  production  of  new  substances,  by  uniting  those  on 
which  it  acts,  is  the  characteristic  effect  of  chemical  attrac- 
tion. In  a  word,  all  chemical  changes  are  effected  by  the 
force  of  chemical  attraction. 

11.     Influence  of  Cohesion  on  Chemical  Action. — 

If  we  place  a  crystal  of  potassium  chlorate,  about  one- 
half  as  large  as  a  grain  of  wheat,  in  contact  with  a  piece  of 
brimstone  of  about  the  same  size,  no  chemical  change  occurs. 
The  particles  of  each  are  held  together  by  cohesion,  and 
kept  from  uniting  with  those  of  the  other.  But  if  we  grind 
them  together  in  a  mortar,  a  sharp  explosion  follows.  The 
chemical  action  converts  both  into  gases,  which  disappear  in 
the  air.  This  experiment  illustrates  the  fact,  that,  in  the 
solid  forms  of  matter,  cohesion  is  generally  too  strong  to  be 
overcome  by  chemical  attraction. 

To  weaken  cohesive  attraction  is  to  facilitate  chemical 
action.  In  the  experiment,  cohesion  was  overcome  by  pul- 
verizing the  solids.  It  may  be  overcome  or  weakened  in 
other  ways,  among  which  solution  and 
fusion  are  most  important. 

Effect  of  Dissolving  the  Sub- 
stances.—  If  sodium  carbonate  and 
tartaric  acid,  both  in  the  finest  pow- 
der, be  mixed  most  thoroughly,  or 
rubbed  together  violently,  no  chemi- 
cal action  will  take  place.  But,  when 
a  little  water  is  added  to  this  mixture, 
a  violent  chemical  action  will  quickly 
follow.  Let  the  mixture  be  made  at 
the  bottom  of  a  tall  jar  (Fig.  8), 
and  the  vigor  of  the  action  will,  very 
likely,  carry  the  foam  to  the  top  and  over  upon  the  plate 
below. 


12  CHEMISTRY. 

Now,  in  this  case,  the  water  by  dissolving  the  solids  has 
overcome  cohesion  to  such  an  extent,  that  chemical  attraction 
can  bring  about  a  chemical  change.  In  this  way  solution 
very  generally  facilitates  chemical  action. 

Effect  of  Fusing1  the  Substances.  —  The  melting  of 
solids  together  often  has  the  same  effect.  If  we  take  a  little 
sulphur,  twice  as  much  potassium  carbonate  (well  dried), 
and  three  times  as  much  niter,  powder  them  well  sepa- 
rately, then  mix  them  thoroughly  on  paper,  and  introduce  a 
little  of  the  mixture  into  an  iron  spoon,  we  may  melt  them 
together  over  the  gas-lamp.  The  cohesion  is  overcome  by 
the  heat ;  and  the  mixture  explodes  violently,  announcing  the 
chemical  action  produced.  In  this  way  fusion  very  generally 
facilitates  chemical  action. 

Exceptions.  —  Yet  we  must  not  suppose  that  no  two 
solids  can  combine  without  their  cohesion  being  first  over- 
come by  the  methods  just  described.  If,  for  example,  a 
crystal  of  iodine  is  laid  upon  a  thin  slice  of  phosphorus,  the 
two  will  shortly  burst  into  a  rapid  and  curious  combustion. 
But  such  examples  are  quite  rare :  the  liquid  form  is  most 
favorable  to  chemical  action. 

12.  Influence  of  Heat.  —  Although  the  liquid  state  is 
most  favorable  to  chemical  action,  yet  in  many  instances  no 
chemical  change  takes  place  until  the  mixture  is  heated.  A 
high  temperature  is  favorable  to  chemical  action. 

We  have  already  seen  the  power  of  heat  to  produce  chemi- 
cal changes.  Sulphur  was  ignited,  before  it  would  combine 
with  oxygen  to  form  sulphurous  oxide.  Mercury  was  heated, 
before  it  would  combine  with  oxygen  to  form  mercuric  oxide. 

Attraction  of  Phosphorus  and  Oxygen.  —  Phosphorus 
and  oxygen  are  two  elements  between  which  there  is  a  pow- 
erful chemical  attraction.  Nevertheless  at  ordinary  tempera- 
ture their  combination  is  very  slow.  Phosphorus  is  kept 
under  water  to  prevent  the  action  of  oxygen  in  the  air,  which 
will  consume  it  slowly  on  exposure,  and  very  rapidly  if  its 


CHEMISTRY.  13 

temperature  be  raised.  The  heat  of  the  fingers  may  start 
the  combustion,  and  hence  phosphorus  must  be  handled  with 
great  caution. 

Rapid  Combination  by  Heat.  —  But  let  us  cut  a  thin 
slice  from  the  end  of  a  stick  of  phosphorus  under  water,  and 
carefully  dry  it  by  very  gentle  pressure  between  two  folds  of 
blotting-paper.  We  may  then  place  it  upon  a  piece  of  card- 
board supported  by  a  test-glass  (Fig.  9).  Delicate  clouds 
of  white  vapor  float  away :  these  are 
the  new  substance  formed  by  the  slow 
combination  of  phosphorus  and  oxy- 
gen at  ordinary  temperature.  Now 
let  a  red-hot  iron  rod  be  brought  near. 
The  phosphorus  will  burst  into  rapid 
combustion,  evolving  large  volumes 
of  dense  white  fumes,  even  while  the 
hot  rod  is  several  inches  away. 

All  these  are  examples  of  chemical  Fig.  9. 

combination  ;  but  heat  very  often  pro- 
duces chemical  decomposition  also.    We  have  already  learned 
that  the  red  mercuric  oxide  is  resolved  into  mercury  and 
oxygen  when  strongly  heated.     Chemical  decomposition  by 
heat  alone  is  called  DISSOCIATION. 

Different  Effects  of  High  and  Low  Temperatures.  — 
The  experiments  with  mercury  and  oxygen  illustrate  another 
curious  and  inportant  fact,  —  that  a  compound  which  is 
formed  only  at  a  high  temperature,  is  again  decomposed  if 
heated  to  a  temperature  still  higher.  In  order  to  compel 
mercury  and  oxygen  to  combine,  we  must  heat  them  almost 
to  the  boiling  point  of  mercury ;  and  then  by  heating  the 
red  oxide  thus  formed  to  a  still  higher  temperature,  we  repro- 
duce the  elements. 

Most  compounds  are  more  readily  made  under  the  influ- 
ence of  high  temperature  ;  and  yet  at  some  higher  tempera- 
ture, it  is  thought,  every  compound  may  be  resolved  into  its 
elements  again. 


14 


CHEMISTKY. 


13.  The  Influence  of  Electricity.  —  Electricity  is  also 
a  powerful  agent  in  chemical  action.  The  decomposition  of 
water  is  an  example.  Many  other  liquids  may  be  decom- 
posed in  a  similar  way.  This  decomposition  by  electricity  is 
called  ELECTROLYSIS. 

In  the  decomposition  of  water  the  oxygen  was  liberated  at 
the  positive  pole  of  the  battery,  and  the  hydrogen  at  the 
negative  pole.  The  oxygen  is  described  as  the  electro-nega- 
tive constituent,  and  the  hydrogen  as  the  electro-positive  con- 
stituent, of  water.  Whenever  a  compound  is  decomposed  by 
electricity,  that  constituent  which  is  found  at  the  negative 
pole  of  the  battery  is  called  the  ELECTRO-POSITIVE  constituent, 
the  other  is  called  the  ELECTRO-NEGATIVE  constituent. 

Chemical  Combination  by  Electricity.  —  But  electri- 
city may  also  produce  chemical  combination. 

The  tall  glass  tube  represented  in  Fig. 
10  is  closed  at  the  top,  and  open  at  the 
bottom.  Two  platinum  wires  are  fused 
into  the  glass  near  the  upper  end :  they 
almost  touch  one  another  on  the  inside. 
The  tube  was  first  filled  with  water. 
Afterwards  a  few  bubbles  of  oxygen 
were  introduced,  and  a  little  more  than 
twice  as  much  hydrogen  was  added. 
Now  let  a  spark  of  electricity  pass 
through  the  gases  by  means  of  the  plat- 
inum wires,  and  a  violent  explosion  in- 
stantly follows.  The  gases  combine 
under  the  influence  of  the  electricity, 
and  disappear,  only  the  small  excess  of 
Fig.  10.  hydrogen  remaining. 

14.  The  Influence  of  Light.  —  Both  decomposition  and 
combination  are  also  brought  about  by  light. 

We  may  witness  an  example  of  decomposition  if  we  will 
dampen  the  surface  of  a  piece  of  paper  with  a  solution  of 


CHEMISTRY. 


15 


silver  nitrate,  and  expose  it  to  the  action  of  the  sunlight. 
Darker  and  darker  the  white  surface  becomes,  until  finally  it 
is  almost  black.  This  darkening  of  the  surface  is  due  to  the 
decomposition  of  the  nitrate  by  light. 

A  large  number  of  compounds  of  silver  are  darkened  by 
light.  The  art  of  photography  is  founded  upon  this  decom- 
posing action  of  light. 

Combination  by  Light.  —  Combination  is  also  brought 
about  by  light,  as  when  hydrogen  and  chlorine  gases  are 
mixed  in  a  glass  vessel.  The  direct  rays  of  the  sun  will  drive 
them  into  combination  so  rapidly  as  to  produce  explosion.  A 
new  gas  —  hydrochloric  acid  gas  —  is  formed  by  their  union. 

Let  a  strong  tube  or  bottle  be  filled  with  a  mixture  of  the 
two  gases,  taking  care  to  have  a  little  more  of  one  —  say  of 
hydrogen  —  than  of  the  other.  Let 
this  mixture  be  prepared  in  a  dark 
room,  the  tube  containing  it  being  in- 
verted in  a  vessel  of  water,  firmly  fixed 
in  place  (Fig.  11),  and  covered  with  a 
black  cloth.  Thus  prepared,  take  the 
apparatus  at  once  to  a  place  where  the 
direct  rays  of  the  sun  may  fall  upon  it, 
and  by  means  of  a  long  handle  remove 
the  cloth.  A  violent  explosion  will 
quickly  follow  :  the  water,  speedily  dis- 
solving the  acid  gas,  will  rise  in  the 
tube,  and  would  strike  the  top  of  it 
with  violence,  did  not  the  excess  of 
hydrogen  act  as  a  cushion  to  prevent  it. 

Exposed  to  diffuse  light,  the  com- 
bination of  the  mixed  gases  is  gradual ;  but,  if  prepared  and 
kept  in  the  dark,  no  combination  occurs. 

These  experiments  clearly  illustrate  the  fact,  that  sunlight 
has  power  to  produce  chemical  action.  Other  intense  lights, 
the  electric  light  for  example,  may  be  used  with  similar 
results. 


Fig.  11. 


16  CHEMISTRY. 


REVIEW. 

L— SUMMARY   OF  PRINCIPLES. 

15.  Attraction  is  a  force  under  whose  influence  bodies  of 
matter  tend  to  approach  one  another. 

Attraction  is  called  gravitation  when  it  acts  between  sepa- 
rate masses  of  matter.  It  is  called  cohesion  when  it  acts 
between  the  particles  of  a  body  without  causing  any  chemical 
change.  It  is  called  chemical  attraction  when  it  causes  two 
or  more  substances  to  produce  a  single  substance  quite  unlike 
themselves. 

Chemical  attraction  is  opposed  by  cohesion.  We  facilitate 
chemical  action  by  reducing  the  strength  of  cohesion. 

Cohesion  may  be  reduced  by  pulverizing  the  solid,  by  dis- 
solving it,  and  by  melting  it.  All  these  processes  are  favor- 
able to  chemical  action. 

Chemical  action  is  most  likely  to  occur  when  the  substances 
are  brought  together  in  the  liquid  form. 

The  application  of  heat  is  favorable  to  chemical  change. 
Electricity  and  light  also,  in  many  cases,  produce  chemical 
action. 

Electrolysis  is  the  decomposition  of  a  compound  by  elec- 
tricity. The  constituents  are  distinguished  as  electro-positive 
and  electro-negative. 

II.  —EXERCISES. 

Define  attraction.  Name  the  three  varieties  of  attrac- 
tion. Define  each.  To  which  of  these  are  chemical  changes 
due? 

What  is  the  influence  of  cohesion  on  chemical  action? 
Why  should  pulverizing  solids  facilitate  their  chemical 
action?  By  what  other  means  may  we  weaken  cohesion? 
Name  two  solids  whose  cohesion  does  not  prevent  their 
combination. 

What  is  the  general  influence  of  heat  on  chemical  action  ? 


CHEMISTRY.  17 

Give  an  example  of  chemical  combination,  brought  about  by 
heat.  Give  an  example  of  chemical  decomposition,  brought 
about  by  heat.  Define  dissociation. 

Give  an  example  of  chemical  decomposition  by  electricity. 
Define  electrolysis.  What  is  meant  by  electro-positive  and 
electro-negative  constituents  ? 

Give  an  example  of  chemical  combination  by  electricity. 

What  is  the  effect  of  light  upon  silver  compounds  ? 

What  is  the  effect  of  light  on  mixed  chlorine  and  hydrogen 


SECTION   III. 

THE  INDESTRUCTIBILITY  OF  MATTER. 

16.  No  Loss  occurs  in  Chemical  Combination.  —  In 

many  cases  of  chemical  action,  substances  disappear  and  seem 
to  be  lost.  This  happens  when  a  candle  burns  :  its  material 
slowly  wastes  awa}T.  Nevertheless,  the  quantity  of  matter 
in  all  such  cases  remains  unchanged.  Much  or  even  all  of 
it  may  become  invisible,  but  by  appropriate  tests  its  existence 
can  be  demonstrated. 

Test  for  the  Presence  of  Matter.  —  Weight  is  the  ap- 
propriate measure  of  the  quantity  of  matter,  and  experiment 
will  always  decide  whether  the  weight  of  the  products  of 
chemical  action  is  exactly  equal  to  that  of  the  substances 
which  take  part  in  it. 

Application  of  this  Test.  —  Take  a  piece  of  phosphorus 
as  large  as  a  pea,  and  support  it  on  top  of  a  small  wire 
whose  lower  end  is  bent  into  a  flat  spiral  so  that  it  will  stand 
upright.  Select  a  thin,  light  beaker,  and  a  large,  thin,  and 
light  flask,  of  about  1,500  cubic  centimeters  capacity.  Put 
about  400  cubic  centimeters  of  water,  colored  blue  with  lit- 
mus, into  the  beaker,  stand  the  phosphorus  wire  in  it,  and 
then  invert  the  flask  over  the  phosphorus,  with  its  neck  rest- 
ing on  and  completely  dosing  the  top  of  the  beaker,  and  its 


18 


CHEMISTRY. 


mouth  reaching  almost  to  the  bottom  of  the  colored  water. 
The  outside  must  be  dry. 

In  this  condition,  let  the  whole  apparatus  be  placed  upon 
one  pan  of  a  pair  of  scales,  and  exactly  balanced  by  weights 
in  the  other  pan.  (Fig.  12.) 

If  we  leave  the  apparatus  for  several  hours, — perhaps 
until  to-morrow, — we  shall  find  that  water  has  risen  into 

the  flask,  as  shown  in  the 
figure,  as  if  a  part  of  the 
air  had  been  annihilated. 
Moreover,  we  think  we  can 
see  that  the  phosphorus  has 
wasted  away,  as  if  a  part 
of  its  substance  also  had 
been  destroyed.  The  bal- 
ance, however,  remains  un- 
disturbed :  the  apparatus 
weighs  exactly  as  much  as 
at  first,  showing  that  no  loss 
can  be  detected.  And  yet, 
if  what  substance  has  disap- 
peared had  been  destroyed,  the  apparatus  would  weigh  at 
least  .43  of  a  gram  less.  A  good  common  balance  would 
easily  detect  much  less  loss  than  that. 

What  has  actually  happened  is  this :  The  phosphorus  has 
combined  with  oxygen,  which  is  one  of  the  constituents  of 
the  air  in  the  flask.  The  compound,  phosphorous  oxide,  is 
aosorbed  by  the  water,  and  remains  unseen.  This  new  sub- 
stance contains  all  the  oxygen  and  all  the  phosphorus  which 
seem  to  have  been  lost. 

In  all  cases  of  chemical  combination,  the  compound  weighs 
exactly  the  same  as  the  constituents  used  up  in  producing  it. 

17.  No  Loss  in  Chemical  Decomposition.  —  In  chemi- 
cal decomposition,  also,  the  quantity  of  matter  remains 
unchanged.  The  red  mercuric  oxide  is  decomposed  by 


Fig.  12. 


CHEMISTRY. 


19 


heat  :  let  us  get  the  facts  by  experiment  with  this  substance. 
We  must  make  the  experiment  so  that  both  constituents  shall 
be  preserved  in  the  apparatus.  (Fig.  13.) 

The  Experiment.  —  Put  about  three  grams  of  the  red 
powder  into  a  small  tube  of  hard  glass,  which  is  provided 
with  a  bent  tube  reaching  just  through  the  cork  of  a  flask  of 
about  two  hundred  cubic  centimeters  capacity.  Let  this  flask 
be  joined  to  another  of  equal  size,  by  means  of  a  bent  tube 


Fig.  13. 


which  reaches  almost  to  its  bottom,  but  only  just  through 
the  cork  of  the  other.  The  first  flask  is  to  be  nearly  or 
quite  full  of  water,  and  must  be  air-tight  at  the  cork  ;  while  the 
second  is  empty  and  loosely  corked.  Place  the  whole  appa- 
ratus, which  should  be  perfectly  dry  outside,  upon  the  scales, 
as  shown  in  the  figure,  and  accurately  balance  it  by  weights. 
Then  heat  the  tube,  and  decompose  the  red  oxide.  The 
powder  will  waste  away ;  globules  of  metallic  mercury  will 
collect  on  the  side  of  the  tube  above  the  heat;  while  the 
oxygen  will  pass  into  the  first  flask,  and  drive  the  water  over 
into  the  second. 

Leave  the  apparatus  at  rest  for  a  time  until  the  tube  has 
become  cold,  and  it  will  be  found  that  the  balance  is  undis- 
turbed. The  whole  weight  is  just  the  same  as  at  first, 


20 


CHEMISTRY. 


showing   that   no   loss  of   matter   has  occurred   during   the 
decomposition. 

General  Results.  —  Many  accurate  experiments  have 
proved  beyond  doubt,  that  matter  is  never  destroyed  nor 
created  by  chemical  action.  During  all  the  chemical  changes 
through  which  substances  may  go,  the  quantity  of  matter  re- 
mains unaltered.  This  is  the  foundation  fact  in  the  science 
of  chemistry. 

18.  Weighing.  —  In  the  study  of  the  chemical  action  of 
the  elements,  and  of  the  properties  of  the  compounds  they 


Fig.  14. 

form,  the  determination  of  the  weights  of  substances  is  an 
operation  of  supreme  importance.  The  chemist  must  do  it 
with  the  utmost  precision.  The  instrument  he  employs  is  the 
chemical  balance  (Fig.  14). 

The  workmanship  in  this  instrument  is  of  the  finest  kind, 
and  the  adjustments  are  made  with  the  nicest  skill.  Heavy 
bodies  are  not  to  be  weighed  in  the  chemical  balance,  but 
the  weight  of  light  ones  can  be  found  with  marvelous  accu- 
racy. With  two  hundred  grams  in  each  scale-pan,  the  in- 
strument shown  in  the  figure  will  turn  by  the  addition  of  the 


CHEMISTET. 


21 


twentieth  of  a  milligram  to  either  side.     One- twentieth  of  a 
milligram  is  about  one  thirteen-hundredth  of  a  grain. 

The  French  or  metric  system  of  weights  is  very  generally 
employed  in  chemistry.  The  student  should  be  familiar  with 
it.  In  this  system 

10  milligrams  =  1  centigram. 

10  centigrams  =  1  decigram. 

10  decigrams   =  1  GRAM          =  15.43-f-grs. 

10  grams          =  1  decagram. 

10  decagrams  =  1  hectogram. 

10  hectograms=  1  kilogram    =  2.2+lbs.  av. 

10  kilograms    =  1  myriagram. 

19.  Measuring.  —  But  when  the  substance  is  a  gas, 
weighing  is  a  difficult  operation,  and  the  quantity  is  usually 
found  by  volume  instead  of  by  weight.  For  this  purpose 
glass  tubes  of  various  sizes  are  accurately  graduated  (Fig. 
11).  The  divisions  along  the  tube  show  the  volume  inside 
in  cubic  inches  or  cubic 
centimeters,  and  frac- 
tions of  these  units. 

Liquids  also  are  more 
easily  measured  than 
weighed,  and  for  many 
purposes  their  volumes 
are  taken  instead  of 
their  weight.  In  Fig. 
15  some  forms  of  grad- 
uated vessels  for  liquids 
are  represented. 

The  cubic  centimeter 
is  the  volume  of  one  gram  weight  of  pure  water  at  4°  C. 
The  number  of  cubic  centimeters,  therefore,  represents  also 
the  weight  of  the  water  in  grams. 

As  to  any  other  liquid,  if  the  number  of  cubic  centimeters 
is  multiplied  by  the  specific  gravity,  the  product  will  represent 
the  weight  of  that  liquid  in  grams. 


Fig.  15. 


22  CHEMISTRY. 

The  cubic  centimeter  is  also  called  milliliter.  It  and  the 
liter  are  the  two  denominations  commonly  used.  The  full 
table  is  as  follows  :  — 

10  milliliters  =  1  centiliter. 

10  centiliters  =  1  deciliter. 

10  deciliters   =  1  LITER      =  .22  gal. 

10  liters          =  1  decaliter. 

10  decaliters  =  1  hectoliter. 

10  hectoliters  =  1  kiloliter. 

10  kiloliters    =  1  myrioliter. 

The  operations  of  weighing  and  measuring  require  many 
precautions,  and  the  exercise  of  much  skill,  to  insure  the 
nicest  accuracy.  We  will  not  here  enter  upon  the  minute 
details. 

REVIEW. 

L  — SUMMARY    OF    PRINCIPLES. 

20.  By  chemical  attraction  substances  are  made  to  com- 
bine. They  disappear  altogether,  but  new  substances  are 
seen  in  their  stead. 

Moreover  the  products  of  chemical  action  are  often  in- 
visible gases. 

Nevertheless  all  the  matter  of  the  original  substance  ex- 
ists in  the  products  of  the  action. 

During  all  chemical  changes  the  quantity  of  matter  remains 
unaltered. 

The  quantity  of  matter  in  a  body  is  found  by  taking  its 
weight,  or  in  the  case  of  gases,  and  often  of  liquids  also,  by 
taking  its  volume. 

Hence  the  operations  of  weighing  and  measuring  are 
fundamental  and  most  important  operations  in  chemistry. 
The  science  is  built  upon  the  data  given  by  them. 

The  French  or  metric  system  of  weights  and  measures  is 
most  largely  employed  in  chemistry. 


CHEMISTRY.  23 


The  milligram,  the  gram,  and  the  kilogram  are  the  three 
most  useful  units  of  weight. 

The  cubic  centimeter  and  the  liter  are  the  most  useful 
units  of  volume.  1,000  milligrams  =1  gram  ;  .1.000  grams  = 
1  kilogram  ;  1,000  cubic  centimeters  =  1  liter. 

II.  —  EXERCISES. 

By  what  means  may  we  find  out  whether  any  gain  or  loss 
occurs  in  chemical  change  ? 

What  are  the  results  of  experiment? 

Of  what  importance  is  the  balance  iff  chemistry  ? 

What  system  of  weights  is  generally  used  ? 

Give  the  table.  What  is  the  value  of  the  gram  in  Eng- 
lish measure  ?  Of  the  kilogram  ? 

How  many  milligrams  in  one  ounce  Troy? 

How.  many  grains  are  equal  to  500  m.  g.  ? 

How  are  the  quantities  of  gases  and  liquids  found? 

What  is  a  cubic  centimeter? 

What  is  the  weight  of  100  cc.  of  alcohol,  whose  specific 
gravity  is  .82? 

What  is  the  English  value  of  the  liter  ? 

Give  the  table  of  volumes  in  the  metric  system. 


SECTION    IV. 

ANALYSIS  AND  SYNTHESIS. 

21.  Analysis.  —  Any  process  by  which  a  compound  may 
be  separated  into  its  constituents,  and  its  composition  de- 
termined, is  called  Analysis.  If  in  the  process  only  the 
names  of  the  constituents  are  found,  the  analysis  is  quali- 
tative; if  their  proportions  are  found,  the  analysis  is  quan- 
titative. 

By  Electricity.  —  Many  substances  may  be  decomposed, 
and  their  composition  found,  by  the  action  of  electricity. 
We  have  already  learned  that  such  a  process  is  called  ELEC- 


CHEMISTRY. 


TROLYSIS.  The  most  interesting  example  of  electrolysis  is 
that  of  water.  Let  us  repeat  the  experiment,  and  study  it 
more  in  detail. 

Two  platinum  strips  are  inserted  in  a  jar  of  water ;  and 
over  them  are  inverted  two  long  and  slender  tubes,  previously 
filled  with  water.  (See  Fig.  16.)  The  wires  of  a  galvanic 
battery  are  then  inserted  in  the  screw  cups,  s  s.  Instantly  a 

torrent  of  gas-bub- 
bles rises  in  each 
tube,  and  will  con- 
tinue to  do  so  until 
the  tubes  are  filled. 
These  two  gases  are 
the  constituents  of 
-  water.  As  the  ex- 
periment goes  on, 
it  will  be  noticed 
that  one  tube  is 
being  filled  faster 
than  the  other  ; 
indeed,  being  of 
equal  size,  one  fills 
twice  as  fast  as  the  other.  If  the  gases  are  tested,  that 
which  is  most  rapidly  set  free  is  found  to  be  hydrogen,  the 
other  oxygen. 

The  experiment  teaches  that  water  is  composed  of  hydro- 
gen and  oxygen,  in  the  proportion  by  volume  of  two  of  hy- 
drogen to  one  of  oxygen. 

Proportions  by  Weight.  —  This  composition  by  volume 
is  shown  directly  by  the  tubes  ;  but,  if  we  desire  to  know  the 
proportions  of  the  gases  by  weight,  we  must  make  a  calcula- 
tion. 

The  specific  gravity  of  oxygen  is  16.  By  this  is  meant 
that  any  volume  of  oxygen  weighs  just  sixteen  times  as  much 
as  an  equal  volume  of  hydrogen.  If,  then,  there  were  equal 
volumes  of  the  two  gases  in  water,  their  proportions  by 


Fig.  16. 


CHEMISTKY.  25 

weight  would  be  as  1  :  16.  Since  there  are  two  volumes  of 
hydrogen,  the  proportions  are  as  2 :  1G.  Eighteen  parts 
of  water  (16  +  2)  contain  sixteen  parts  of  oxygen  and  two 
parts  of  hydrogen.  This  being  the  ratio,  it  is  easy  to  find 
just  what  part  of  any  quantity  of  water  is  hydrogen,  and  what 
part  oxygen.  For  example :  one  hundred  of  water  must 
contain  \°B°-x  2  =  11. 11  of  hydrogen,  and  if£x  16  =  88.89  of 
oxygen. 

Percentage  Composition.  —  The  composition  of  a  com- 
pound is  usually  given  by  the  hundred,  and  it  is  then  called 
the  PERCENTAGE  COMPOSITION.  The  results  in  the  case  of 
water  are  written  in  this  way  :  — 

WATER. 

Hydrogen 11.11 

Oxygen 88.89 

100.00 

By  the  Prism.  —  When  the  light  of  a  burning  substance 
is  passed  through  a  prism,  it  is  decomposed  ;  and  the  appear- 
ance of  the  spectrum  depends  upon  the  nature  of  the  burning 
substance.  Hence  the  constituents  of  a  compound  may  be 
told  by  the  appearance  of  its  spectrum.  This  method  of 
detecting  the  presence  of  substances  is  called  SPECTRUM 
ANALYSIS. 

For  example :  when  the  spectrum  of  burning  sodium  is 
viewed  through  a  telescope,  a  bright  yellow  line,  of  surpris- 
ing brilliancy,  is  seen  in  the  yellow  part  of  the  spectrum. 
Or,  if  potassium  is  burned,  a  single  crimson  line  and  another 
of  blue,  both  of  great  beauty,  will  be  seen  in  opposite  ends 
of  the  spectrum.  Nor  will  the  appearance  of  either  set  be 
changed  by  the  presence  of  the  other ;  for,  if  a  mixture  of 
sodium  and  potassium  is  burned,  the  observer  will  see  both 
sets  in  the  same  spectrum,  their  place,  size,  and  brightness 
the  same  as  when  each  was  formed  alone.  The  spectra  of 
many  elements  have  been  carefully  studied ;  they  can  be 


26  CHEMISTRY. 

easily  recognized  by  one  who  has  previously  made  their  ac- 
quaintance. 

By  Chemical  Action.  —  The  methods  of  analysis  just 
described  are  limited  in  application.  The  general  method  is 
by  the  chemical  action  of  bodies  upon  each  other.  More 
than  a  hint  of  this  method  would  be  out  of  place  here.  But 
suppose,  for  example,  that  a  solution  of  unknown  substances 
in  water  is  to  be  analyzed.  A  few  drops  of  hydrochloric 
acid  may  be  added.  If  a  white,  solid  substance  is  formed, 
it  shows  the  presence  of  either  silver,  mercury,  or  lead.  To 
find  out  which  of  these  metals  is  present,  a  little  ammonia  is 
added :  if  the  solid  disappears  again,  the  metal  is  silver ;  if 
it  simply  turns  black,  mercury  is  present ;  but  if  it  remains 
unchanged,  the  metal  is  lead.  If  the  acid  fails  to  produce 
the  white  solid,  or  PRECIPITATE,  as  any  solid  formed  in  this 
way  from  solution,  by  the  action  of  chemicals,  is  called,  then 
these  three  metals  are  counted  absent,  and  some  other  agent 
is  used  by  which  another  group  of  metals  may  be  detected. 

So  far  the  analysis  is  only  qualitative.  To  obtain  quanti- 
tative results,  the  balance  must  be  used. 

The  original  substance  is  first  weighed,  and  finally  the 
precipitate,  clean  and  pure  and  dry.  These  two  weights 
enable  the  chemist  to  calculate  the  weight  of  the  metal  in 
one  hundred  parts  of  the  original  compound. 

22.  Synthesis.  —  The  composition  of  a  compound  may  be 
found  by  causing  its  constituents  to  combine,  and  noticing 
the  proportions  required.  This  process  is  called  SYNTHESIS. 
The  synthesis  of  water  may  illustrate :  it  may  be  made  in 
an  apparatus  called  a  EUDIOMETER. 

This  instrument  is  a  glass  tube,  open  at  one  end,  and  care- 
fully graduated,  having  two  metallic  wires  passing  through 
the  glass  near  the  closed  end,  and  almost  touching  each 
other  inside.  To  use  it,  measured  quantities  of  hydrogen 
and  oxygen,  say  fifty  volumes  of  each,  are  put  into  it.  The 
tube  should  still  be  much  less  than  full  of  the  mixed  gases, 


CHEMISTRY. 


27 


and  should  be  firmly  held  with  its  open  end  in  the  cistern. 

(Fig.    17.)       If    now   electricity   from   a   Leyden-jar  or   a 

Ruhmkorff-coil  is  passed  through  the  mixture,  the  two  gases 

combine  with  violent   explosion ;    water  will   be   formed  by 

their  union  ;  and  water  or  mercury  from  the  cistern  will  rise 

into  the  tube  to  fill  the  space 

they  occupied.     The  quantity 

of  gas  left  will  be  found   to 

be  twenty-five  volumes,  and, 

if  tested,  will  be  found  to  be 

oxygen. 

It  is  evident  that  fifty  vol- 
umes of  hydrogen  have  taken 
twenty-five  volumes  of  oxygen 
to  form  water  ;  and  the  experi- 
ment therefore  teaches  that 
water  is  composed  of  hydro- 
gen and  oxygen  in  the  pro- 
portions by  volume  of  two  of 
hydrogen  to  one  of  oxygen.  Fig.  17. 

By  analysis  or  by  synthesis, 

the  chemist  is  able  to  find  out  just  what  all  kinds  of  matter 
are  composed  of,  and  even  the  exact  proportions  by  weight 
or  by  volume,  in  which  their  constituents  are  united. 


REVIEW. 

I.— SUMMARY   OF  PRINCIPLES. 

23.  The  composition  of  a  compound  may  be  found  by 
analysis  or  by  synthesis. 

Analysis^  is  any  process  by  which  a  compound  is  sepa- 
rated into  constituents,  and  its  composition  determined. 

Svjxtbeeis^is  any  process  by  which  the  constituents  of  a 
compound  may  be  made  to  combine  and  produce  it. 


28  CHEMISTRY. 

Qualitative  analysis  is  an  analysis  in  which  only  the  names 
of  the  constituents  are  found. 

Quantitative  analysis  is  an  analysis  in  which  the  propor- 
tions by  volume  or  by  weight  of  the  constituents  are  deter- 
mined. 

By  the  percentage  composition  of  a  compound,  we  mean 
the  proportional  parts  of  all  its  constituents  in  one  hundred 
parts  of  the  compound. 

In  one  hundred  ounces,  grams,  or  other  units,  by  weight, 
of  water,  there  are  88.89  ounces,  grams,  or  other  units  of 
oxygen,  and  11.11  of  the  same  units  of  hydrogen. 

By  volume,  however,  water  consists  of  two  volumes  hydro- 
gen to  one  volume  oxygen. 

A  precipitate  is  any  solid  substance  produced  by  the 
chemical  action  of  other  substances  in  solution. 

In  the  solution  of  a  compound  of  either  silver,  mercury,  or 
lead,  hydrochloric  acid  will  produce  a  white  precipitate,  and 
in  these  only. 

Hydrochloric  acid  is  said,  therefore,  to  be  a  TEST  for  the 
presence  of  these  metals. 

Conversely,  any  compound  of  these  metals  is  a  test  for 
hydrochloric  acid.  If  a  solution  contains  the  slightest  quan- 
tity of  this  acid,  a  drop  or  two  of  silver  nitrate  will  turn  it 
white. 

II.— EXERCISES. 

Define  analysis.  Define  qualitative  analysis.  Define  quan- 
titative analysis.  Describe  the  electrolysis  of  water.  What 
does  this  analysis  of  water  show  ? 

Define  specific  gravity.  What  is  the  specific  gravity  of 
oxygen?  Knowing  that  water  consists  of  one  volume  oxy- 
gen and  two  volumes  hydrogen,  how  would  you  calculate 
the  proportions  by  weight?  Define  percentage  composition. 
What  is  the  percentage  composition  of  water? 

Define  spectrum  analysis.  What  is  a  more  general  method 
of  analysis  ?  Define  precipitate.  How  would  you  tell  which 


CHEMISTRY.  29 

of  the  metals,  silver,  mercury,  or  lead,  is  contained  in  a  sub- 
stance? How  would  you  find  out  how  much  the  original 
substance  contained? 

Define  synthesis.     Describe  the  eudiometer.     What  does 
the  synthesis  of  water  teach? 


SECTION  V. 

THE  LAWS  OF  COMBINATION. 

24.  The   Law  of   Constant   Proportions.  —  The    first 
great  law  discovered  by  the  use  of  the  balance  and  the  meas- 
uring tube  is  that  of  the  invariable  proportions  of  the  con- 
stituents in  any  chemical  compound.     Whether  we  find  the 
composition  of  water  by  analysis  or  by  synthesis  ;  whether 
we  operate  upon  water  from  the  clouds,  from  the  spring,  or 
from  any  other  source,  —  we  find  it  to  consist  of  the  same 
elements,  and  in  the  same  proportions  by  weight  or  volume 
The  same  may  be   said   of  every  other  known   compound. 
The  law  states,  that  — 

The  same  compound  is  always  made  up  of  the  same  con- 
stituents^ combined  in  the  same  definite  proportions.  This  is 
known  as  the  law  of  ' '  definite  "  or  of  "  constant  propor- 
tions." 

25.  Composition   of   Hydrochloric   Acid.  —  We    may 

study  the  combination  of  hydrogen  and  chlorine  by  experi- 
ment, and  determine  their  constant  proportions  in  hydrochloric 
acid. 

The  Experiment.  —  Let  us  provide  a  small  cistern,  partly 
full  of  a  strong  solution  of  common  salt.  Let  us  fill  two 
graduated  tubes  (Fig.  18)  also  with  this  brine,  and  invert 
them  in  the  cistern.  Into  one  of  these  we  may  pass  up  20 
cubic  centimeters  of  hydrogen  and  40  cubic  centimeters  of 
chlorine.  Into  the  other  we  will  pass  20  cubic  centimeters 
of  chlorine  and  40  cubic  centimeters  of  hydrogen.  All  this 


30 


CHEMISTRY. 


having  been  done  quickly,  we  at  once  place  the  whole  appa- 
ratus for  five  minutes  in  direct  sunlight.  Now,  chlorine  is 
a  greenish-yellow  gas,  which  will  extinguish  the  flame  of  a 
match ;  while  hydrogen  is  a  colorless  gas,  which  takes  fire 

instantly  on  contact  with  the 
flame. 

Finally  it  will  be  seen  that 
only  20  cubic  centimeters  of 
gas  remain  in  each  tube. 
That  in  the  first  tube  is 
greenish-yellow,  and  if  tested 
will  extinguish  a  flame  :  it  is 
chlorine.  That  in  the  second 
tube  is  colorless,  and  if  tested 
will  take  fire  :  it  is  hydrogen. 
The  Result  by  Volume. 
—  The  20  cubic  centimeters 
of  hydrogen  in  the  first,  com- 
bined with  20  cubic  centi- 
meters of  chlorine.  The  20 
cubic  centimeters  of  chlorine 
in  the  second,  combined  with 
20  cubic  centimeters  of  hydrogen.  The  proportions  by  vol- 
ume, in  both  cases,  are  1:1.  We  can  not  make  these  two 
gases  combine  in  any  other  proportions.  The  composition 
of  hydrochloric  acid  is,  invariably,  hydrogen  and  chlorine  in 
equal  volumes. 

The  Result  by  Weight.  —  Now,  the  weights  of  equal 
volumes  of  these  gases  are  as  1  to  35.5  :  hence  the  composi- 
tion of  hydrochloric  acid  by  weight  is  1  of  hydrogen  to  35.5 
of  chlorine.  These  proportions  are  invariable. 

Hydrochloric  acid  always  consists  of  these  same  elements, 
combined  in  these  same  proportions. 

26.  Combining  Weights.  —  So  definite  and  constant  are 
the  weights  of  the  elements  in  combination,  that  a  number 


Fig.  18. 


CHEMISTRY.  31 

is  attached  to  each,  which  is  called  its  COMBINING  WEIGHT. 
It  represents  the  smallest  relative  proportion,  by  weight,  in 
which  the  element  can  unite  with  others  to  form  compounds. 
For  example,  it  is  found  that  any  given  weight  of  hydrogen 
must  have  at  least 

35.5  times  as  much  chlorine  to  form  a  compound. 
80        "  "          bromine      "  " 

127        "  "          iodine          "  " 

These  numbers  are  the  combining  weights  of  chlorine, 
bromine,  and  iodine,  because  they  are  the  weights  of  the 
smallest  quantities  of  these  elements  which  can  combine  with 
a  unit  weight  of  hydrogen. 

Again,  if  we  examine  some  other  compounds  of  chlorine, 
we  find  that 

C    39  of  potassium, 

35.5  of  chlorine  must  have  J    23  of  sodium, 

(  108  of  silver. 

These  numbers  are  the  combining  weights  of  potassium, 
sodium,  and  silver,  because  they  are  the  smallest  relative 
quantities  of  these  elements  which  can  enter  into  combina- 
tion. 

The  Unit  of  Combining  Weights.  —  Hydrogen  is  the 
standard  of  comparison  for  combining  weights.  Any  given 
weight  of  hydrogen  may  be  regarded  as  the  unit.  35.5 
times  that  is  the  smallest  weight  of  chlorine,  and  108  times 
that  weight  is  the  smallest  weight  of  silver,  which  can  com- 
bine without  excess  of  either.  Thus  every  element  has  a 
numerical  value  in  chemical  change.  These  combining 
weights  are  to  be  found  in  the  table  of  elements  on  p.  53. 

27.  The  Law  of  Multiple  Proportions.  —  Each  ele- 
ment has  but  one  combining  weight,  and  yet  the  same  two 
elements  may  form  more  than  a  single  compound. 

Some  Facts.  —  Of  oxygen  and  nitrogen,  for  example,  no 
less  than  five  compounds  are  known  to  exist.  Examine  their 
composition,  and  another  law  will  be  brought  to  light. 


32  CHEMISTRY. 

.(1)  (2)  (3)  (4)  (5) 
Nitrogen  28  14  28  14  28 
Oxygen  16  16  48  32  80 

Now  16  is  the  combining  weight  of  oxygen  ;  and  we  find 
in  this  series  that  when  the  quantity  of  oxygen  is  not  16  it 
is  some  multiple  of  16. 

Again,  14  is  the  combining  weight  of  nitrogen  ;  and  we 
also  find,  that  when  the  quantity  of  nitrogen  is  not  14  it  is  a 
multiple  of  14. 

The  Law.  —  This  illustrates  the  law,  that  if  one  element 
unites  with  another,  in  more  than  one  proportion,  these  pro- 
portions will  all  be  multiples  of  its  combining  weight. 

If  we  attempt  to  combine  these  elements  in  any  other  pro- 
portions, the  result  will  be  that  all  of  one  of  them  will  be 
used  up  to  form  one  or  more  of  these  five  compounds,  while 
the  excess  of  the  other  will  be  left  uncombined. 

28.  The   Combining  Weight   of   a   Compound. —  A 

compound  must  contain  the  same  quantity  of  matter  as  its 
constituents  :  this  follows  from  the  indestructibility  of  mat- 
ter. Water  contains  two  parts  of  hydrogen  and  sixteen 
parts  of  oxygen.  Its  numerical  value  must  therefore  be 
16  -{-2:=  18.  Moreover,  water  combines  with  many  other 
substances,  and  its  combining  weight  is  found  to  be  18. 

This  illustrates  the  law,  that  the  combining  weight  of  a 
compound  is  the  sum  of  the  combining  proportions  of  its 
constituents. 

Combining  Proportions.  —  It  is  important  to  notice  that 
the  term  "combining  proportion,"  just  now  used,  does  not 
mean  combining  weight  in  all  cases.  The  combining  weight 
of  hydrogen  is  1  :  the  quantity  which  combines  with  16  of 
oxygen,  however,  is  2  ;  and  it  is  this  which  enters  into  the 
combining  weight  of  water.  We  have  applied  the  term 
' '  combining  weight ' '  to  the  smallest  proportion  of  any  sub- 
stance which  may  enter  into  combination  :  we  apply  the  term 
"oombining  proportion"  to  the  relative  weight  actually 


CHEMISTRY.  33 

existing  in  the  compound.  Thus  the  combining  weight  of 
oxygen  is  1C  :  its  combining  proportion  is  sometimes  16,  and 
sometimes  32  or  48  or  80,  or  some  other  multiple  of  16. 

29.  Dalton's  Theory.  —  John  Dalton,  in  the  year  1808, 
declared  his  belief  that  the  combining  weights  of  the  ele- 
ments are  simply  the  relative  weights  of  the  very  smallest 
particles  of  them  which  can  enter  into  chemical  action. 

We  may  divide  a  body  into  a  multitude  of  pieces.  Indeed, 
we  may  grind  it  to  the  finest  dust,  and  it  may  seem  that  there 
is  no  end  to  its  divisibility.  But  Dalton's  theory  assumes 
that  there  is  a  point  beyond  which  we  can  not  carry  the  divis- 
ion, and  that  when  we  reach  this  point  we  have  minute 
particles  whose  weights  are  not  alike  in  different  elements. 
These  ultimate  particles  of  the  elements  are  called  ATOMS. 
The  chemist  defines  the  atom  to  be  the  smallest  portion  of  an 
dement  which  can  take  part  in  a  chemical  action. 

According  to  this  theory,  an  atom  of  oxygen  weighs  sixteen 
times  as  much  as  an  atom  of  hydrogen ;  and,  in  the  same 
way,  the  combining  weights  of  chlorine,  sodium,  silver,  and 
of  other  elements,  tell  us  how  many  times  the  atoms  of  these 
bodies  are  heavier  than  an  atom  of  hydrogen.  Hence  the 
terms  c '  combining  weights  ' '  and  ' '  atomic  weights  ' '  mean 
the  same  thing. 

Dalton's  theory  assumes  also  that  chemical  action  is  an 
action  among  atoms,  that  chemical  attraction  acts  upon  the 
atoms  of  elements,  and  brings  them  together  to  produce  the 
compound. 

This  theory  is  known  as  the  ATOMIC  THEORY. 

Reason  for  Accepting  this  Theory.  —  The  atomic 
theory  is  generally  believed ;  for,  while  it  is  impossible  to  get 
at  these  atoms  to  weigh  them  separately,  to  handle  them,  or 
to  see  them,  still  it  seems  impossible  to  discover  any  good 
reason  for  the  laws  of  combination,  unless  they  do  exist.  On 
the  other  hand,  if  we  admit  the  existence  of  atoms,  it  is  per- 
fectly clear  that  the  weights  of  the  elements  in  a  compound 


34  CHEMISTRY. 

must  be  definite  and  constant.  That  theory  in  science  is 
accepted,  which  gives  a  clear  and  complete  explanation  of  all 
the  facts  which  it  embraces.  This  the  atomic  theory  seems 
to  do,  and  this  is  the  evidence  of  its  truth. 

30.  The  Molecule.  —  When  hydrogen  and  chlorine  com- 
bine to  form  hydrochloric  acid,  each  atom  of  chlorine  seizes 
an  atom  of  hydrogen.     In  a  tube  full  of  the  compound,  we 
have   simply   a   multitude   of   these   pairs   of   atoms.     The 
smallest  quantity  of  hydrochloric  acid  which  can  be,  must, 
according  to  this  theory,  consist  of  these  two  atoms.     So, 
common  salt  is  a  compound  of  chlorine  and  sodium,  and  the 
smallest  piece  of  it  which  can  exist  as  salt,  must  contain  two 
atoms,  one  of  chlorine  and  one  of  sodium.     These  ultimate 
particles  of  a  compound  are  called  MOLECULES. 

It  is  believed  that  the  atoms  of  the  elements,  also,  when 
they  are  in  the  free  state,  that  is,  not  in  combination,  are 
linked  together  in  groups,  generally  of  two ;  and  so  the 
chemist  defines  the  molecule  to  be  the  smallest  particle  of  an 
element  or  compound  which  can  exist  in  the  free  state. 

31.  Combination  by  Volume.  —  We   have  learned  al- 
ready that  it  is  more  easy  to  measure  gases  than  to  weigh 
them.     But  the  question  arises,  How  much  by  volume  of  the 
gases  must  be  taken  in  order  to  produce  compounds  without 
leaving  any  part  of   either  constituent   uncombined?     This 
question  is  answered  by  the  law  of  Gay  Lussac,  discovered 
by  him  in  1808.     It  states  that  "  the  weights  of  the  combining 
volumes  of  the  gaseous  elements  bear  a  simple  relation  to  their 
atomic  weights." 

To  find  this  Relation.  —  This  simple  relation  is  found 
by  the  balance.  By  weighing  equal  volumes  of  these  ele- 
ments it  is  found  that  — 

1  liter  of  oxygen  weighs  1 6  times  as  much  as  a  liter  of  hydro- 
gen. 

1  liter  of  nitrogen  weighs  14  times  as  much  as  a  liter  of 
hydrogen. 


CHEMISTRY.  35 

1  liter  of  chlorine  weighs  35.5  times  as  much  as  a  liter  of 

hydrogen. 

Here  we  see  that  these  weights  of  equal  volumes  are  the 
same  as  the  atomic  weights  of  the  elements.  This  is  true  of 
nearly  all  the  elements  when  in  the  form  of  gas  or  vapor. 

If,  then,  we  bring  such  elements  together  in  equal  volumes, 
or  in  some  multiple  of  the  equal  volume,  it  will  be  the  same  in 
effect  as  bringing  them  together  in  the  proportions  of  their 
combining  weights  or  in  some  multiple  of  their  combining 
weights  :  no  excess  of  either  can  remain  after  combination 
has  taken  place. 

The  Volume  of  the  Compound.  —  Experiments  show 
further  that  the  simple  relation  extends  to  the  volume  of  the 
compound  also.  The  following  are  some  of  the  results  of 
exact  experiment :  — 

1  vol.  chlorine  and  1  vol.    hydrogen  form  2  vols.  hydrochloric  acid. 
1  vol.  bromine  and  1  vol.    hydrogen  form  2  vols.  hydrobromic  acid. 
1  vol.  iodine      and  1  vol.    hydrogen  form  2  vols.  hydriodic  acid. 
1  vol.  oxygen    and  2  vols.  hydrogen  form  2  vols.  steam. 
1  vol.  nitrogen  and  3  vols.  hydrogen  form  2  vols.  ammonia. 

We  here  find  that  two  volumes  of  the  compound  are 
formed  in  every  case  ;  and  we  discover  the  curious  fact,  that, 
whether  the  sum  of  the  constituent  volumes  be  2  or  3  or  4, 
the  volume  of  the  compound  is  only  2.  It  is  found  in  other 
cases  also,  that,  whatever  the  number  of  volumes  which  enter 
into  combination,  the  volume  of  the  resulting  compound 
is  2. 

Avogaclro's  F^aw.  —  The  simplest  explanation  we  can 
find  of  these  facts  is  based  upon  two  assumptions,  viz.  :  — 

Every  molecule  of  each  of  these  elementary  gases  contains 
two  atoms. 

Equal  volumes  of  all  gases,  simple  and  compound,  contain 
an  equal  number  of  molecules. 

Let  us  study  the  case  of  steam  in  the  above  table,  remem- 
bering that,  according  to  the  atomic  theory,  two  atoms  of  hy- 
drogen and  one  atom  of  oxygen  form  one  molecule  of  steam. 


36  CHEMISTRY. 

If  each  molecule  of  oxygen  contains  two  atoms  of  oxygen, 
and  only  one  is  needed  in  a  molecule  of  steam,  there  will  be 
just  twice  as  many  molecules  of  steam  produced  as  there  are 
of  oxygen  required  to  form  it.  And  then  if  equal  volumes  of 
steam  and  oxygen  contain  the  same  number  of  molecules, 
twice  as  many  molecules  of  steam  must  fill  just  twice  the 
volume  of  the  oxygen.  Hence  the  combination  of  one  vol- 
ume of  oxygen  with  sufficient  hydrogen  must  produce  two 
volumes  of  steam.  The  same  kind  of  reasoning  explains  all 
other  cases,  and  hence  it  is  believed  that  the  assumptions  on 
which  the  explanations  are  founded  are  true. 

The  supposition  that  "Equal  volumes  of  all  gases,  simple 
and  compound,  contain  equal  numbers  of  molecules, ' '  was  first 
made  by  Avogadro  in  1811.  It  is  known  as  AVOGADRO'S 
LAW,  and  is  generally  accepted,  both  in  chemistry  and  in 
physics. 

REVIEW. 

L  — SUMMARY  OP  PRINCIPLES. 

32.  Chemical  changes  occur  in  obedience  to  certain  laws, 
known  as  the  laws  of  combination. 

The  "  Law  of  Constant  Proportions  "  states  that  the  same 
compound  is  always  made  up  of  the  same  constituents,  com- 
bined in  the  same  definite  proportions  by  weight. 

Water  always  consists  of  hydrogen  and  oxygen  in  the 
proportions,  by  weight,  of  two  of  hydrogen  and  sixteen  of 
oxygen. 

Hydrochloric  acid  always  consists  of  hydrogen  and 
chlorine,  in  the  proportions,  by  weight,  of  one  of  hydrogen 
to  35.5  of  chlorine. 

The  combining  weights  of  substances  are  the  smallest 
relative  proportions,  by  weight,  in  which  they  enter  into 
combination. 

Hydrogen  is  the  standard  of  combining  weights  ;  any  given 
weight  of  this  gas  may  be  considered  the  UNIT. 


CHEMISTRY.  87 

The  "Law  of  Multiple  Proportions"  states,  that  if  one 
substance  unites  with  another,  in  more  than  one  proportion, 
these  proportions  are  all  multiples  of  its  combining  weight. 

The  combining  weight  of  a  compound  is  the  sum  of  the 
combining  proportions  of  its  constituents. 

The  combining  weight  of  water  is  eighteen,  of  hydro- 
chloric acid  36.5. 

These  laws  of  combination  have  been  established  by 
experiment.  Our  knowledge  of  them  is  quite  independent  of 
any  theory.  Still  the  theory  proposed  by  Dalton  does  explain 
them. 

This  "Atomic  Theory"  assumes  that  every  element  con- 
sists of  ATOMS,  or  minute  particles,  the  smallest  that  can 
take  part  in  any  chemical  action.  It  assumes  further,  that 
any  compound  is  formed  by  the  union  of  the  atoms  of  its 
elements,  and  that  the  combining  weights  of  the  elements 
are  the  relative  weights  of  their  atoms. 

A  MOLECULE  is  the  smallest  particle  of  an  element,  or  of 
a  compound,  which  can  exist  in  the  free  state. 

Chemical  change  consists  in  the  breaking  up  of  old  mole- 
cules, and  the  re-arrangement  of  their  atoms  to  form  new 
ones. 

A  molecule  of  hydrochloric  acid  contains  one  atom  of 
hydrogen  and  one  of  chlorine.  A  molecule  of  water  con- 
tains two  atoms  of  hydrogen  and  one  of  oxygen.  A  mole- 
cule of  ammonia  contains  four  atoms,  three  of  hydrogen  and 
one  of  nitrogen. 

A  molecule  of  an  element  generally  contains  two  atoms. 

Combining  volumes  are  the  relative  proportions  by  volume 
in  which  gaseous  0r  volatile  substances  unite. 

The  weights  of  the  combining  volumes  of  the  elementary 
gases  bear  a  simple  ratio  to  their  atomic  weights.  This  is 
Gay  Lussac's  Law. 

Equal  volumes  of  all  gases,  elementary  or  compound,  at 
the  same  temperature  and  pressure,  contain  an  equal  number 
of  molecules.  This  is  Avogadro's  Law. 


38  CHEMISTEY. 

According  to  this  law,  the  molecules  of  all  gases  or  vapors 
are  of  the  same  size.  That  is,  the  molecular  volumes  of  all 
gases,  elementary  or  compound,  are  equal :  the  numerical 
value  is  two. 

Combining  volume,  combining  or  atomic  weight,  specific 
gravity,  and  molecular  weight,  are  all  referred  to  hydrogen 
as  a  standard  of  comparison. 

Let  us  represent  the  names  of  a  few  elements  by  their 
initial  letters,  and  under  each  put  its  numerical  values.  We 

shall  have 

H      O      N  P         Hg. 

1 —    1 —    1 —       •£ —     2 = combining  vols. 

Weights  of  these  =  1  —  16  —  14  —  31   —  200= atomic  weights. 

Weights  of  equal  vols.  =  1  —  16  —  14  —  62   —  100= specific  gravities. 
Mol.  of  H  =  2  atoms        2  —  32  —  28  —  124   —  200= molecular  weights. 

2—2—2—  2—     2= molecular  vols. 

From  that  we  discover  that  — 

Atomic  weight  =  specific  gravity  X  combining  volume  : 

Molecular  weight  =  2  x  specific  gravity. 

II.— EXERCISES. 

What  is  the  composition  of  water?  What  is  the  compo- 
sition of  hydrochloric  acid,  by  volume?  By  weight?  Is 
it  always  the  same  ?  Is  the  same  thing  true  of  other  sub- 
stances? State  the  law  of  constant  proportions. 

Define  combining  weight.  What  is  the  unit  of  measure 
for  combining  weights  ?  The  combining  weight  of  chlorine 
is  35.5  :  what  is  meant  by  this  statement? 

Ten  grams  of  hydrogen  will  require  how  much  chlorine  to 
convert  it  all  into  hydrochloric  acid  ? 

What  would  be  the  result  if  ten  grams  hydrogen,  mixed 
with  360  grams  chlorine,  are  exposed  to  sunlight? 

If  100  cubic  centimeters  of  oxygen  are  mixed  with  100 
cubic  centimeters  of  hydrogen,  what  will  remain  after  pass- 
ing the  electric  spark  through  the  mixture  ? 

If  100  grams  of  oxygen  are  to  be  converted  into  water, 
how  much  hydrogen  must  be  used  ? 


CHEMISTEY.  39 

How  many  compounds  of  oxygen  and  nitrogen  are  known? 
What  law  do  their  compositions  illustrate?  State  this  "law 
of  multiple  proportions." 

What  is  the  combining  weight  of  water?  State  the  law 
which  this  illustrates. 

Define  atom.  Define  molecule.  What  is  the  atomic 
theory?  On  what  ground  is  the  atomic  theory  accepted? 

State  Gay  Lussac's  Law.  Compare  the  weights  of  one 
liter  of  each, — oxygen,  nitrogen,  and  hydrogen.  What 
relation  between  these  weights  and  the  atomic  weights  of 
these  elements?  Define  combining  volume.  What  is  the 
combining  volume  of  a  gaseous  or  volatile  compound  ? 

State  Avogadro's  Law. 

How  much  oxygen  is  required  to  unite  with  10  liters  of 
hydrogen  ? 

How  many  liters  of  water-vapor  will  be  formed  by  the 
union  of  2,000  cubic  centimeters  of  hydrogen  and  1,000  cubic 
centimeters  of  oxygen  ? 

Are  the  combining  volumes  of  the  elements  the  relative 
volumes  of  their  atoms,  or  of  their  molecules? 


SECTION  VI. 

CHEMICAL  NOTATION  AND  NOMENCLATURE. 

33.  Symbols.  —  Instead  of  writing  the  names  of  elements 
in  full,  chemists  have  agreed  to  use  a  set  of  symbols  to  rep- 
resent them.  These  symbols  are  the  capital  initial  letters  of 
the  names  (often  of  the  Latin  names) ,  or,  in  case  two  ele- 
ments have  the  same  initial,  this  capital  with  a  small  letter 
added.  Thus  O  stands  for  oxygen  ;  N  for  nitrogen  ;  H  for 
hydrogen.  Of  carbon,  cobalt,  and  copper  (Latin  cuprum}, 
the  symbols  are  C,  Co,  and  Cu.  The  symbol  not  only  repre- 
sents the  name  of  the  element:  it  also  represents  just  one 
atom  of  it.  The  symbols  of  all  the  elements  are  given  in  the 
table  on  p.  53. 


40  CHEMISTEY. 

34.  Formulas  of  Compounds.  —  Instead  of  writing  the 
names  of  compound  bodies  in  full,  a  system  of  formulas  has 
been  adopted.  The  formula  of  a  compound  is  made  up  of 
the  symbols  of  its  constituents,  with  figures  placed  a  little 
below  to  show  the  number  of  combining  weights.  Instead 
of  writing  the  statement  that  water  consists  of  hydrogen  and 
oxygen,  two  combining  weights  of  the  one  to  one  of  the 
other,  we  may  with  less  trouble  write  the  formula,  H2  O, 
which  teaches  the  same  thing.  That  nitric  acid  consists  of 
one  part  of  hydrogen,  one  of  nitrogen,  and  three  of  oxygen, 
is  shown  by  the  simple  expression,  H  N  O3.  When  no 
figure  is  used,  one  is  understood.  The  formula  not  only 
represents  the  name :  it  also  represents  just  one  molecule  of 
the  compound. 

What  they  teach.  —  These  formulas  contain  much  valu- 
able information  about  the  compounds  they  represent. 

They  teach  :  — 

1st,  The  names  of  the  constituents,  by  the  letters  they 
contain. 

2d,  The  number  of  combining  weights  of  each,  by  the 
figures  they  contain. 

3d,  The  number  of  combining  volumes  of  gaseous  or 
volatile  constituents,  also  by  the  figures  they  contain. 

4th,  The  combining  proportion  of  each,  for  this  is  equal 
to  the  combining  weight  multiplied  by  the  figures  used. 

5th,  The  number  of  atoms  of  each  element  in  the  molecule 
of  the  compound. 

Illustration.  —  The  formula  of  potassium  chlorate,  for 
example,  is  K  Cl  O3,  and  it  answers  all  of  the  following 
questions  :  — 

1st,  What  are  the  constituents  of  this  compound?  Potas- 
sium, chlorine,  and  oxygen. 

2d,  How  many  combining  weights  of  each?  One  of 
potassium,  one  of  chlorine,  three  of  oxygen 

3d,  How  many  volumes  of  each  ?  One  of  potassium,  one 
of  chlorine,  three  of  oxygen. 


CHEMISTRY. 


41 


4th,  What  combining  proportion  of  each?  K  =  39.1, 
Cl  =  35.5,  O  =  48. 

5th,  How  many  atoms  in  one  of  its  molecules?  One  of 
potassium,  one  of  chlorine,  and  three  of  oxygen. 

CHEMICAL  NOMENCLATURE. 

35.  The  Nomenclature.  —  Not  until  the  year  1787  was 
any  attempt  made  to  reduce  the  language  of  chemistry  to  a 
system.     But  the   number  of    compounds   to   be   described 
increased  to  such  an  extent  that  even  the  strongest  memory 
could  not  hope  to  keep  their  meaningless  names.     To  avoid 
this  difficulty,  a  system  was  proposed  by  Lavoisier,  by  which 
the  name  of  a  substance  should  indicate  its   composition. 
The  simplicity  of  the  system,  and  the  accuracy  with  which  it 
expressed  chemical  theories,  secured  its  universal  adoption ; 
but  the  theories  themselves  having  now,  in  great  part,  been 
rejected,  new  names  have  been  introduced,  and  it  can  not 
yet  be  said  that  the  system  is  permanent.      Nevertheless, 
certain  specific  rules  are  observed.     The  object  is  to  make 
the   name   of    a   com- 
pound show  what  ele- 
ments it  is   composed 

of,  and,  as  nearly  as 
may  be,  also  the  rela- 
tive proportions  in 
which  they  are  present. 

36.  Binary     Com- 
pounds. — When  only 
two     elements     unite, 
they  form  what  is  called 
a   BINARY  COMPOUND. 
Among   the   most  nu- 
merous and  important  are  the  binary  compounds  of  oxygen. 

For  example,  let  a  piece  of  magnesium,  which  can  be  had 
in  the  form  of  wire  or  ribbon,  be  held  in  a  pair  of  forceps, 


Pig.  19. 


42  CHEMISTRY. 

while  the  other  end  is  heated  in  the  flame  of  a  lamp.  The 
metal  first  becomes  red-hot,  and  then  takes  fire  (Fig.  19). 
It  burns  with  a  vivid  light,  and  throws  off  large  volumes  of 
white  smoke.  This  white  smoke  is  the  compound  of  oxygen 
with  magnesium.  It  is  called  MAGNESIUM  OXIDE. 

In  like  manner  all  the  binary  compounds  of  oxygen  are 
called  OXIDES,  while  the  other  part  of  the  name  signifies  the 
element  with  which  the  oxygen  is  united. 

Prefixes.  —  It  often  happens  that  oxygen  forms  several 
binaries  with  the  same  other  element,  by  combining  in  mul- 
tiple proportions.  This  is  true  with  the  metal  manganese. 
Three  distinct  oxides  of  manganese  are  known.  Their 
formulas  are :  — 

Mn  O    .     .     .     1  atom  of  O  in  the  molecule. 
Mn  O2  .     .     .     2  atoms    "         "  " 

Mn2O3.     .     .     3      "        "         "  " 

To  show  that  one  atom  of  oxygen  is  present  in  the  mole- 
cule, the  first  is  called  manganese  monoxide.  The  two 
atoms  of  oxygen  in  the  second  are  indicated  by  the  name 
manganese  d/oxide  ;  while  the  proportions  three  to  two  atoms 
in  the  molecule  of  the  third  are  shown  by  the  name  mangan- 
ese sesquioxide. 

In  general,  we  may  say  that  the  number  of  combining 
weights,  or  of  atoms,  in  the  molecule,  is  shown  by  a  prefix  to 
that  part  of  the  name  which  represents  the  element. 

The  prefix  mon  may  be  omitted  ;  the  term  oxide  alone 
indicating  the  monoxide.  And  often  the  prefix  per  is  given 
in  the  name  of  the  oxide  which  has  the  largest  proportion  of 
oxygen,  without  regard  to  the  number  of  atoms. 

Terminations.  —  In  case  the  same  element  forms  two 
oxides,  it  is  customary  to  use  the  terminations  ic  and  ous  in 
naming  them.  Thus  sulphur  and  oxygen  form 

S  O8      ....       sulphuric  oxide. 
S  O2      ....     sulphurows  oxide. 


CHEMISTRY.  43 

And  the  two  compounds  of  mercury  and  oxygen  are  called 
mercuric  oxide,  Hg  0,  and  mercurous  oxide,  Hg2  O. 

Still  these  same  substances  may  be  named  by  the  use  of 
prefixes  ;  and  then,  in  the  case  of  sulphur,  we  have,  for  the 
first,  sulphur  trioxide,  and,  for  the  second,  sulphur  dioxide. 
In  very  many  other  cases,  also,  the  same  compound  may 
have  two  or  more  different  names. 

Other  Binary  Compounds.  —  The  very  same  rules  for 
naming  these  oxygen  compounds  apply  to  the  naming  of  the 
binaries  of  many  other  elements,  such  as  chlorine  and 
sulphur.  Thus,  for  example  :  — 

Compounds  of  are  called  such  as  formula 

Chlorine,  chlorides,  sodium  chloride,  Na  Cl. 

Bromine,  bromides,  potassium  bromide,  K  Br. 

Iodine,  iodides,  lead  iodide,  Pb  I2. 

Sulphur,  sulphides,  iron  sulphide,  Fe  S. 

The  same  prefixes,  and  the  terminations  ic  and  ous,  are 
used  for  exactly  the  same  purposes  in  naming  these  as  in 
naming  the  oxides. 

37,  Acids,  and  their  Composition.  —  If   we    place    a 

piece  of  dry  phosphorus  upon  a 
little  support,  resting  on  a  dry 
plate,  touch  it  with  a  hot  wire,  and 
quickly  invert  over  it  a  dry  bell- jar 
(Fig.  20),  the  burning  phosphorus 
will  throw  off  large  volumes  of  milk- 
white  vapors,  much  of  which  will 
finally  condense  into  snow-like  flakes 
upon  the  sides  of  the  glass. 

In   this   experiment   the   oxygen 
of   the   air,    and    the    phosphorus, 
unite  to  form  the  new  white  sub- 
stance, —  the  phosphorous  pentox-  Flg'  20* 
ide,  whose  formula  is  P2  O5  —  a  binary  compound. 

Next,  let  the  jar  be  lifted,  and  a  little  water  poured  into  it. 


44  CHEMISTRY. 

The  water  combines  with  the  white  oxide,  which  disappears 
with  a  hissing  sound.  The  fluid  becomes  intensely  sour  to 
the  taste ;  and  if  a  little  of  this  solution  be  added  to  a 
solution  of  blue  litmus,  the  blue  color  will  be  instantly  changed 
to  red. 

This  power  to  redden  blue  litmus,  or  other  vegetable  colors, 
is  characteristic  of  an  all-important  class  of  compounds 
called  ACIDS.  The  water  and  the  oxide  combined  to  form 
PHOSPHORIC  ACID. 

Composition  of  Acids.  —  The  composition  of  this  phos- 
phoric acid  is  shown  by  its  formula  :  H3  P  O4.  Its  molecule 
contains  three  atoms  of  hydrogen,  one  of  phosphorus,  and 
four  of-  oxygen.  Below  are  the  formulas  of  several  other 
acids  for  inspection  :  — 

Sulphurous  acid,  H2  S  O3.  Hydrochloric  acid,       H  Cl. 

Sulphuric  acid,    H2  S  O4.  Hydrobromic  acid,      H  Br. 

Nitric  acid,  H  N  O3.  Hydriodic  acid,  H  I. 

Carbonic  acid,      H2  C  O3.  Hydrosulphuric  acid,  H2  S. 

A  glance  at  these  formulas  reveals  the  fact  that  hydrogen 
is  a  constituent  in  every  one  of  these  acids. 

From  all  these  facts  we  may  gather  this  description  :  viz., 
an  acid  is  a  hydrogen  compound,  which  is  generally  sour  to 
the  taste,  and  which  will  redden  vegetable  colors. 

They  are  of  Two  Classes.  —  Another  glance  at  the  above 
formulas  reveals  the  fact  that  some  acids  contain  oxygen, 
and  that  others  do  not.  Those  which  contain  oxygen  are 
called  OXYGEN  ACIDS,  or  Ox  ACIDS  ;  while  those  which  do  not 
are  called  HYDRACIDS.  The  oxygen  acids  comprise  far  the 
larger  number  of  this  class  of  bodies. 

38.  Names  of  the  Oxygen  Acids.  —  The  terminations 
ic  and  ous  are  used  in  the  names  of  the  oxygen  acids,  signi- 
fying the  same  thing  as  when  used  in  the  names  of  binaries. 
That  is,  the  ic  indicates  the  larger  proportion  of  oxygen  in 
the  molecule.  Thus,  for  example,  H  N  O3  is  nitric  acid, 


CHEMISTRY.  45 

while  H  N  02  is  nitrous  acid.  Two  acids  of  sulphur  are 
distinguished  in  the  same  way. 

The  prefix  hypo  is  also  used,  and  always  means  less. 
Hypomtrous  acid,  for  example,  is  one  which  contains  a  still 
smaller  proportion  of  oxygen  than  the  nitrous  acid :  its 
formula  is  H  N  O.  The  prefix  per  is  also  sometimes  used 
to*  form  the  name  of  the  acid  which  contains  the  largest  pro- 
portion of  oxygen. 

Names  of  the  Hydracids.  —  The  names  of  the  hydra- 
cids  also  end  in  £c,  but  they  are  especially  characterized  by 
the  prefix  hydro.  Find  this  prefix  in  the  names  of  acids  in 
the  list  already  given.  These  four  are  the  most  important 
acids  of  this  class,  and  the  name  shows  the  constituents  in 
each. 

The  hydrogen  acids  are  really  binary  compounds,  and  we 
may  name  them  as  such  if  we  choose.  Instead  of  hydro- 
chloric acid,  we  may  speak  of  H  Cl  as  hydric  chloride. 

39.  Salts.  —  Notice  the  following  experiment.  Into  a 
bottle  put  a  few  clippings  of  zinc,  and  upon  them  pour  a 
quantity  of  hydrochloric  acid.  A  vigorous  boiling  quickly 
begins  ;  hydrogen  gas  escapes,  and  may  be  set  on  fire  with 
a  match  ;  the  zinc  slowly  disappears,  and  finally  a  quiet  liquid 
remains,  which  would  be  quite  clear  but  for  some  black 
residue  from  the  impurities  of  the  zinc  employed.  By 
evaporating  the  clear  liquid  we  may  obtain  a  white  solid : 
this  proves  to  be  zinc  chloride. 

The  explanation  is  this  :  The  zinc  has  decomposed  the  acid, 
taking  the  place  of  the  hydrogen  which  was  in  combination 
with  the  chlorine.  Before  the  action  we  had  hydric  chloride 
and  zinc :  after  the  action  we  have  zinc  chloride  and  hy- 
drogen. 

Atoms  of  zinc  take  the  place  of  atoms  of  hydrogen  in  the 
molecules  of  the  acid.  This  zinc  chloride  is  not  only  a  binary 
compound :  it  is  also  called  a  SALT.  If  sodium  takes  the 
place  of  hydrogen  in  the  same  acid,  the  salt,  sodium  chloride 
(common  salt) ,  is  formed. 


46  CHEMISTRY. 

Again :  if  the  two  combining  weights  of  hydrogen  in 
sulphuric  acid  are  both  replaced  by  sodium,  a  salt,  sodium 
sulphate,  will  be  formed ;  or,  if  only  one  of  them  is  replaced 
by  sodium,  the  remaining  compound  is  still  a  salt.  From 
these  illustrations  we  gather  this  description :  A  salt  is  a 
compound  formed  by  substituting  a  metal  for  either  the  whole 
or  a  part  of  the  hydrogen  in  an  acid.  * 

40.  Names  of  Salts.  —  The  salts  formed  from  hydracids 
are  named  by  the  method  already  given  for  neutral  binary 
compounds.  These  salts  were  formerly  called  haloid  salts. 

Names  of  Oxy-Salts.  —  Of  salts  formed  from  oxacids, 
the  name  is  made  by  changing  the  ending  of  the  name  of 
the  acid  from  which  they  are  derived,  from  ic  to  ate,  or  from 
ous  to  ite. 

A  few  examples  will  make  this  method  clear. 

Salts  from  are  such  as 

Sulphuric  acid,  sulphates,  sodium  sulphate. 

Sulphurous  acid,  sulphites,  sodium  sulphite. 

Nitric  acid,  nitrates,  potassium  nitrate. 

Nitrous  acid,  nitrites,  potassium  nitrite. 

Chloric  acid,  chlorates,  potassium  chlorate. 

Chlorous  acid,  chlorites,  sodium  chlorite. 

Hypochlorous  acid,  hypochlorites,       sodium  hypochlorite. 

In  case  only  a  part  of  the  hydrogen  of  the  acid  is  dis- 
placed, the  presence  of  the  remainder  is  indicated  in  the 
name  by  the  prefix  hydro.  When,  for  example,  all  the 
hydrogen  of  sulphuric  acid  H2  S  O4  is  replaced  by  sodium, 
the  salt  Na2  S  O4  is  called  sodium  sulphate ;  but,  if  only  one 
of  the  two  combining  weights  of  hydrogen  is  displaced,  the 
presence  of  the  metal  and  of  the  remaining  hydrogen  is 
shown  by  the  name  hydro-sodium  sulphate  H  Na  S  O4. 

In  the  same  way  potassium  and  sulphuric  acid  may  form 
either  potassium  sulphate  or  hydro-potassium  sulphate. 

The  acids  are  sometimes  called  HYDROGEN  SALTS.     Just 


CHEMISTRY. 


47 


as  K  N  03  is  called  potassium  nitrate,  so  H  N  O3  may  be 
called  hydrogen  nitrate  instead  of  nitric  acid. 

41.  Bases.  —  Let  a  small  piece  of  the  metal  potassium 
be  dropped  upon  the  surface  of  water  :  it  instantly  takes  fire 
(Fig.  21),  runs  swiftly  about  over  the 
surface  of  the  water,  until  finally  it  is 
all  wasted  away.  If  now  we  prepare 
some  reddened  litmus,  by  adding  to  blue 
litmus  a  few  drops  of  "acid,  and  after- 
ward add  some  of  the  water  on  which 
the  potassium  burned,  we  find  that  the 
blue  color  of  the  litmus  is  quickly  re- 
stored. 

The   power   to   neutralize    an    acid, 
shown  by  the  restoration  of   the   blue 
color  to  reddened  litmus,  is  characteristic  of  another  large 
and  important  class  of  compounds.     They  are  called  BASES. 

Hydrates.  —  This  whole  class  of  bodies  also  receives  the 
name  of  HYDRATES.  A  hydrate  is  a  compound  of  hydrogen 
and  oxygen,  with  a  third  element,  usually  a  metal.  It  is 
often  caustic  to  the  taste,  and  restores  the  blue  color  of 
reddened  litmus.  A  hydrate  receives  the  name  of  the  metal 
which  it  contains.  We  have,  accordingly,  sodium  hydrate, 
Na  H  O  ;  potassium  hydrate,  K  H  0  ;  silver  hydrate,  Ag  H  O  ; 
and  lead  hydrate,  Pb  H2  O2,  or,  as  it  is  oftener  written, 
Pb  (HO)2. 


Fig.  21. 


REVIEW. 

L— SUMMARY    OF   PRINCIPLES. 

42.  The  symbol  of  an  element  is  the  capital  initial  of  its 
name,  sometimes  accompanied  by  a  small  letter ;  as,  C  for 
carbon,  and  Co  for  cobalt. 

The  symbol  represents  not  only  the  name,  but  also  a  single 
atom,  of  the  element. 

~0»  THS 


48  CHEMISTRY. 

The  formula  of  a  compound  consists  of  the  symbols  of  its 
elements,  with  small  figures  attached,  to  show  the  number  of 
combining  weights  of  each. 

The  formula  represents  a  single  molecule  of  the  compound. 

Among  the  many  classes  of  compounds  are  binaries,  acids, 
salts,  and  hydrates. 

The  name  of  a  binary  compound  is  known  by  its  terminat- 
ing in  ide.  Besides  this  its  name  combines  the  names  of 
both  constituents,  and  prefixes  are  used  to  show  how  many 
atoms  of  the  constituents  are  present. 

Acids  are  hydrogen  compounds,  which  are  sour,  which  are 
able  to  redden  vegetable  colors,  and  which  will  exchange 
hydrogen  for  a  metal  in  chemical  action. 

Acids  are  called  oxacids  if  they  contain  oxygen,  and 
hydracids  if  they  do  not. 

The  oxacids  are  named  after  the  element  which  is  com- 
bined with  their  hydrogen  and  oxygen,  the  terminations  ic 
and  ous  being  used  to  indicate  larger  and  smaller  proportions 
of  oxygen.  The  prefix  hypo  is  also  used  to  indicate  a  smaller 
proportion  of  oxygen,  and  per  to  show  a  larger  proportion 
of  the  same  element. 

The  prefix  hydro  characterizes  the  name  of  a  hydracid. 
These  acids  may  also  be  named  as  if  they  were  simply  binary 
compounds. 

Salts  are  described  as  substances  which  may  be  produced 
by  substituting  atoms  of  metal  for  atoms  of  hydrogen  in  an 
acid. 

They  are  named  after  the  acids  from  which  they  are 
derived,  by  changing  the  ending  of  the  name  of  the  acid 
from  ic  to  ate,  and  from  ous  to  tie.  The  name  of  the  metal 
is  then  prefixed. 

Acids  are  sometimes  regarded  as  hydrogen  salts,  and  are 
named  as  such.  Instead  of  sulphuric  acid,  we  may  use  the 
name  hydrogen  sulphate. 

Hvrl rates  or  Rases  are  described  as  compounds  of  hydro- 
gen and  oxygen  with  jijnetal  having  the  power  to  neutralize 


CHEMISTRY.  49 

an  acid.     They  are  usually  caustic  to  the  taste,  and  restore 
the  blue  color  of  reddened  litmus. 

The  hydrates  are  named  after  the  metals  which  they 
contain. 

II.  —EXERCISES. 

Define  symbol.     Formula. 

How  much  of  an  element  does  a  symbol  represent? 

How  much  of  a  compound  does  a  formula  represent? 

How  many  atoms  in  a  molecule  of  alcohol,  its  formula 
being  C2H6O? 

What  is  the  symbol  of  Hydrogen  ?     Oxygen  ?     Nitrogen  ? 

How  would  you  represent  a  molecule  of  each  ? 

Define  binary  compound. 

What  are  oxides  ?     How  is  any  oxide  named  ? 

What  is  a  Monoxide  ?  A  Dioxide  ?  A  Trioxide  ?  A  Ses- 
quioxide  ?  A  Peroxide  ? 

For  what  purpose  are  the  terminations  ic  and  ous  used  ? 

What  are  Iodides  ?     Chlorides  ?     Bromides  ?     Sulphides  ? 

Mercury  combines  with  oxygen  ;  what  shall  we  call  the 
compound?  Ans.  Mercuric  oxide. 

But  there  is  another  oxide  of  this  metal,  containing  a  less 
proportion  of  oxygen  ;  what  shall  it  be  named  ? 

What  are  the  elements  of  cupric  oxide  ? 

What  are  the  elements  of  cuprous  oxide  ? 

What  are  the  elements  and  their  proportions  in  chromium 
trioxide  ? 

Name  the  compound  of  potassium  and  iodine. 

Name  the  compound  of  lead  and  sulphur. 

Name  the  compound  of  lead  and  iodine. 

Name  the  compound  of  copper  and  chlorine. 

What  are  the  elements  in  arsenic  sulphide? 

What  are  the  elements  in  zinc  sulphide  ? 

What  is  the  difference  between  cupric  chloride  and  cuprous 
chloride  ? 

What  is  an  acid?     Name  and  distinguish  the  two  classes. 


50  CHEMISTRY. 

What  terminations  are  used  in  naming  the  oxygen  acids? 
What  do  they  indicate  ? 

What  prefixes  are  used  ?     What  do  they  indicate  ? 

What  are  the  constituents  of  phosphoric  acid  ? 

Ans.  Hydrogen,  oxygen,  and  phosphorus. 

By  what  part  of  the  name  is  each  one  of  these  elements 
suggested  ? 

What  are  the  constituents  of  bromic  acid  ? 

Name  the  elements  in  sulphurous  acid. 

Name  the  elements  in  hyposulphurous  acid. 

What  difference  in  the  composition  of  the  last  two  acids 
named,  is  indicated  by  their  names  ? 

What  difference  in  composition  is  indicated  by  the  names 
iodic  acid  and  per-iodic  acid? 

What  acid  will  be  formed  by  the  union  of  hydrogen,  oxy- 
gen, and  bromine  ? 

Name   the  acid  which  contains  oxygen,  manganese,  and 
hydrogen.  Ans.  Manganic  acid. 

What  other  acid  with  the  same  elements,  but  with  a  larger 
proportion  of  oxygen? 

What  are  the  elements  in  hydrofluoric  acid? 

Name  the  elements  in  hydriodic  acid. 

Name  the  elements  in  hydrosulphuric  acid. 

What  is  the  difference  in  composition  of  hydrosulphuric 
acid  and  sulphuric  acid? 

Name  the  acid  compound  of  hydrogen  and  iodine. 

What  is  a  salt  ?     Haloid  salts  ?     What  are  oxy-salts  ? 

How  are  the  haloid  salts  named? 

How  are  the  oxy-salts  named  ? 

Name  the  salt  from  nitric  acid  and  potassium. 

Name  the  salt  from  copper  and  sulphuric  acid. 

Name  the  salt  from  hypochlorous  acid  and  sodium. 

Name  the  acid  and  the  metal  from  which  calcium  carbon- 
ate may  be  derived. 

Name  the  acid  and  the  metal  from  which  calcium  hypo- 
sulphite may  be  derived. 


CHEMISTRY.  OI 

What  are  the  elements  in  ferrous  sulphate  ? 

What  are  the  elements  in  barium  sulphite? 

Of  what  elements  is  magnesium  carbonate  composed  ? 

What  acid  is  required  with  copper  to  form  copper  nitrite  'f 

What  are  the  constituents  of  potassium  chlorate  ? 

Name  the  metal  in  the  aluminium  silicate. 

Name  the  metal  and  the  acid  in  magnesium  citrate. 

Name  the  elements  in  calcium  phosphate. 

What  are  the  constituents  of  hydrogen  sulphate? 

What  other  name  may  be  given  to  the  same  compound  ? 

Name  nitric  acid  as  a  salt.     Chloric  acid.     Acetic  acid. 

Define  base.     What  other  name  is  given  to  this  class? 

How  are  the  hydrates  named? 

What  group  of  atoms  occurs  in  the  molecule  of  every 
hydrate  ?  Ans.  H  O. 

What  are  the  elements  of  calcium  hydrate? 

What  are  the  elements  of  magnesium  hydrate? 

What  are  the  elements  of  copper  hydrate? 

Name  the  elements  of  silver  hydrate. 

Name  the  hydrate  containing  barium.  What  other  ele- 
ments does  it  contain  ? 


52  CHEMISTBY. 


CHAPTER  II. 
THE  NON-METALLIC  ELEMENTS. 


SECTION   I. 
GENERAL  DESCRIPTION. 

43.  The  Number  of  the  Elements.  —  The  elements  are 
those  simple  substances  which,  up  to  the  present  time,  have 
not  been  decomposed.     The  existence  of  sixty-four  has  been 
established,  and  very  recent  researches  seem  to  show  that 
the  existence  of  six  or  seven  more  is  extremely  probable. 

These  few  elements  are  the  alphabet  of  chemistry.  They 
are  united  in  pairs,  or  in  greater  numbers,  to  form  the  solid, 
liquid,  and  gaseous  matter  of  the  entire  globe. 

Not  even  all  of  this  small  number  are  found  abundantly. 
The  greater  part  of  the  whole  mass  of  our  earth  is  made  up 
of  less  than  half  a  score  of  these  elements,  while  some  of 
the  others  are  of  such  rare  occurrence  as  to  be  of  little 
interest  except  to  the  chemist. 

44.  The  following  table  contains  the  sixty-four  elements, 
arranged  in  alphabetical  order,  with  their  symbols  and  atomic 
weights,  for  future  reference. 

To  the  chemist  in  his  nice  researches,  the  most  exact  values 
of  atomic  weights,  which  it  is  possible  to  obtain,  are  impor- 
tant ;  to  the  student,  and  for  purposes  of  illustration,  an 
approximate  value,  the  nearest  whole  number,  is  usually 
sufficient. 

The  exact  value  for  sodium,  for  example,  is  22.99,  but  for 
all  practical  purposes  the  atomic  weight  of  this  element  is  23. 


CHEMISTRY. 


53 


NAMES. 

Symbols. 

Atomic 
Weight. 

NAMES. 

Symbols. 

Atomic 
Weight. 

Aluminium 

Al 

27.3 

Mercury    . 

Hg 

199.8 

Antimony 

Sb 

122.0 

Molybdenum 

Mo 

95.6 

Arsenic 

As 

74.9 

Nickel  .     . 

Ni 

58.6 

Barium 

Ba 

136.8 

Niobium    . 

Nb 

94.0 

Beyllium   . 

Be 

9.0 

Nitrogen   . 

N 

14.01 

Bismuth    . 

Bi 

210.0 

Osmium    . 

Os 

198.6 

Boron   .     . 

B 

11.0 

Oxygen      . 

0 

15.96 

Bromine    . 

Br 

79.75 

Palladium 

Pd 

106.2 

Cadmium  . 

Cd 

111.6 

Phosphorus 

P 

30.96 

Caesium 

Cs 

133.0 

Platinum  . 

Pt 

196.7 

Calcium     . 

Ca 

39.9 

Potassium 

K 

39.04 

Carbon  .     . 

C 

11.97 

Rhodium  . 

Rh 

104.1 

Cerium.     . 

Ce 

141.2 

Rubidium  . 

Rb 

85.2 

Chlorine    . 

Cl 

35.37 

Ruthenium 

Ru 

103.5 

Chromium 

Cr 

52.4 

Selenium  . 

Se 

78.0 

Cobalt  .     . 

Co 

58.6 

Silver    .     . 

Ag 

107.66 

Copper  .     . 

Cu 

63.0 

Silicon  .     . 

Si 

28.0 

Didymium 

Di 

147.0 

Sodium 

Na 

22.99 

Erbium 

Er 

169.0 

Strontium. 

Sr 

87.2 

Fluorine    . 

F 

19.1 

Sulphur     . 

S 

31.98 

Gallium     . 

Ga 

t 

Tantalum  . 

Ta 

182.0 

Gold      .     . 

Au 

196.2 

Tellurium 

Te 

128.0 

Hydrogen  . 

H 

1.0 

Thallium  . 

Tl 

203.6 

Indium 

In 

113.4 

Thorium   . 

Th 

231.5 

Iodine  .     . 

I 

126.53 

Tin  ... 

Sn 

117.8 

Iridium 

Ir 

196.7 

Titanium  . 

Ti 

48.0 

Iron  .     .     . 

Fe 

55.9 

Tungsten  . 

W 

184.0 

Lanthanum 

La 

139.0 

Uranium  . 

U 

240.0 

Lead     .     . 

Pb 

206.4 

Vanadium 

V 

51.2 

Lithium     . 

Li 

7.01 

Ytrium  .     . 

Y 

93.0 

Magnesium 

Mg 

23.94 

Zinc  .     .     . 

Zn 

64.9 

Manganese 

Mn 

54.8 

Zirconium 

Zr 

90.0 

It  is  well  to  remember  that  the  chemist  defines  an  element 
to  be  a  substance  which  has  never  yet  been  decomposed.  He 
does  not  claim  to  know  that  these  sixty-four  kinds  of  matter 
are  really  the  ultimate  simples  of  material  bodies.  Indeed, 
the  science  of  Spectrum  Analysis,  in  the  hands  of  Mr. 
Lockyer,  is  giving  some  reason  for  supposing  that  they  are 
in  reality  compounds  of  still  more  elementary  forms.  It  is 
not  impossible  that  more  powerful  analyses  may  yet  decom- 
pose them. 


54  CHEMISTRY. 

45.  Metals  and  Non-Metals.  —  The  elements  are  usually 
divided  into  two  classes,  —  the  metals,  and  the  non-metals  or 
metalloids.     The  first  includes  such  substances  as  iron,  gold, 
silver,   and   copper ;  the   second,  such   as   sulphur,  oxygen, 
nitrogen,  and  hydrogen.     This  division  is  purely  arbitrary. 
It  is  not  found  in  nature,  but  is  made  for  the  convenience 
of    study.      No   line   of    division   can   distinctly  mark   the 
separation  between  the  metals  and  the  non-metals.     Several 
elements,  of  which  arsenic   is   one,  have  neither   distinctly 
metallic  nor  non-metallic  properties. 

46.  Classification.  —  The    non-metals   are   divided    into 
four   groups.     This   division   is    founded    on    the    relation 
between  the  number  of  their  atoms  which  may  enter  a  mole- 
cule  together.      This   relation   is   seen    by   comparing    the 
formulas  of 

Hydrochloric  acid        .         .         .         .  Cl  H, 

Water O  H2, 

Ammonia    .         .         .         .         .  N  H3, 

Marsh-gas C  H4, 

for  in  them  we  see  that  one  atom  of  chlorine  can  hold  but 
one  atom  of  hydrogen  in  the  molecule,  while  one  atom  of 
oxygen  is  able  to  hold  two,  one  of  nitrogen  three,  and  one 
of  carbon  four. 

Now,  an  atom  of  chlorine  is  never  known  to  combine  with 
more  than  one  of  hydrogen.  We  must  consider  it  equivalent 
to  one  of  hydrogen.  So  we  say  that  an  atom  of  oxygen  is 
equivalent  to  two  atoms  of  hydrogen,  that  one  of  nitrogen 
is  equivalent  to  three,  and  one  of  carbon  is  equivalent  to  four 
of  hydrogen. 

To  express  this  different  equivalence,  — 

Chlorine  is  called  a  univalent  element  or  a  monad. 
Oxygen  "         bivalent         "          "    dyad. 

Nitrogen         "         trivalent        "          "    triad. 
Carbon  "         quadrivalent'4          "    tetrad. 


CHEMISTRY.  55 

The  Groups.  —  But  chlorine  is  not  the  only  element 
whose  atom  is  equivalent  to  one  of  hydrogen  :  there  are 
bromine,  iodine,  and  fluorine  besides.  And  these  four  are 
grouped  together,  and  called  the  UNIVALENT  GROUP  of  non- 
metals. 

Others  are  like  oxygen,  and  with  it  form  the  BIVALENT 
GROUP:  they  are  sulphur,  selenium,  and  tellurium.  In  the 
same  way  we  have  the  TRIVALENT  GROUP,  consisting  of  nitro- 
gen, phosphorus,  arsenic,  and  boron  ;  and  the  QUADRIVALENT 
GROUP,  containing  only  carbon  and  silicon.  These  four 
groups  include  all  the  non-metals. 

Quantivalence.  —  Thus  the  atoms  of  the  different  ele- 
ments have  different  values  in  chemical  change.  The  atom 
of  hydrogen  is  the  unit  by  which  to  measure  these  atomic 
values.  What  is  the  value  of  a  chlorine  atom  ?  One  unit, 
because  it  is  able  to  bind  only  one  atom  of  hydrogen  in  a 
molecule.  For  a  similar  reason,  the  atom  of  any  bivalent 
substance  has  a  value  of  two  units,  of  a  trivalent  substance 
three  units,  and  of  a  quadrivalent  substance  four  units. 

This  atomic  value  of  a  substance  is  called  its  QUANTIV- 
ALENCE. We  accordingly  say  that  the  quantivalence  of 
chlorine  is  1,  that  of  oxygen  2,  of  carbon  4.  And  we  may 
define  quantivalence  to  be  the  combining  power  of  a  sub- 
stance as  measured  by  the  number  of  hydrogen  atoms,  or 
their  equivalent,  which  one  of  its  atoms  can  bind  together  in 
a  molecule. 

47.  Graphic  Symbols  and  Formulas.  —  The  quantiv- 
alence of  an  element  is  represented  by  Roman  numerals, 
or  by  primes  or  dashes  attached  to  its  symbol.  For  ex- 
ample :  — 

1  univalent  atom  of  chlorine       .        .        .     Cl1    or    CF    or      Cl — . 
1  bivalent          "         oxygen        .        .        .     O"    or    O7/    or   — O — . 

1  trivalent        "         nitrogen      .        .        .    Njii  or    W"  or   — N" — . 
1  quadrivalent "         carbon         .        .        .    Civ    or    C""  or    —  C— . 


56  CHEMISTRY. 

The  symbol  of  an  element  with  its  quantivalence  shown 
by  dashes  attached  to  it  is  a  GRAPHIC  SYMBOL. 

The  formula  for  a  compound  may  then  be  made  to  show 
whether  all  the  unit  values  of  its  elements  are  satisfied,  and 
in  what  way.  For  example,  in  the  molecule  of  water  an 
atom  of  oxygen  holds  two  of  hydrogen.  Put  the  symbols 
of  hydrogen  and  oxygen  together  in  this  way,  H — 0 — H, 
and  we  see  that  each  of  the  two  unit  values  of  the  oxygen  is 
balanced  by  a  unit  value  of  hydrogen.  A  similar  formula  for 

Hydrochloric  acid  is  written    ....       H— Cl, 

H 
I 
Ammonia  is  written H— N— H, 

H 
Marsh-gas  is  written H — C — H, 

H 

in  which  we  can  see  how  every  unit  of  quantivalence  of  Cl, 
of  N,  and  of  C,  is  balanced  by  a  unit  of  hydrogen.  Such 
formulas  are  called  GRAPHIC  FORMULAS. 

Unsaturated  Molecules.  —  There  is  a  compound  of 
carbon  and  nitrogen  called  cyanogen.  Its  molecule  contains 
one  atom  of  each  element,  and  its  common  formula  is  there- 
fore C  N.  Its  graphic  formula  is  N  =  C — .  This  graphic 
formula  shows  at  a  glance  that  three  of  the  four  units  of  the 
carbon  atom  are  balanced  by  the  three  units  of  the  nitrogen 
atom,  and  the  fourth  is  unbalanced  or  free.  A  molecule 
like  this,  in  which  there  is  one  or  more  unbalanced  units  of 
quantivalence,  is  called  an  UNSATURATED  molecule ;  while  a 
molecule  like  that  of  water,  in  which  all  the  units  of  quan- 
tivalence are  balanced,  is  said  to  be  SATURATED. 

The  quantivalence  of  a  molecule  is  the  number  of  its 
unbalanced  units.  Thus  the  quantivalence  of  cyanogen, 
N^C— ,  is  1,  while  that  of  water,  H— O— H,  is  0. 

Constitutional  Formula.  —  Now,  these  graphic  formulas 
tell  us  something  about  the  way  in  which  the  atoms  are  put 
together  to  make  a  molecule.  For  instance,  in  the  formula  for 


CHEMISTRY.  57 

water,  H — O — H,  it  appears  that  the  atom  of  oxygen  binds 
the  two  atoms  of  hydrogen  to  itself.  The  hydrogen  atoms 
do  not  seem  to  be  bound  to  one  another  at  all.  Nor  can 
they  be.  Let  ns  try  to  make  the  molecule  by  binding  them 
together,  and  we  have  H — H  and  — O — ,  but  the  quantiv- 
alence  of  the  hydrogen  is  already  exhausted :  there  is  not 
a  single  unit  left  free  by  which  it  can  bind  the  oxygen. 

H 

So  in   the   molecule   of   marsh-gas,  H— C— H,  the  carbon 

H 

atom  must  be  the  nucleus  about  which  the  hydrogen  atoms 
are  arranged. 

Since  these  graphic  formulas  show  what  is  believed  to  be 
the  way  in  which  the  atoms  are  grouped  to  constitute  a  mole- 
cule, they  are  called  CONSTITUTIONAL  FORMULAS. 

Caution.  —  We  must  not  for  a  moment  suppose  that 
these  formulas  show  the  shapes  of  the  molecules,  or  the 
geometrical  arrangement  of  the  atoms  in  them.  We  are  not 
to  infer  that  the  molecule  of  water  is  a  line  of  atoms 

/H 
H — O — H  :  it  may  be  a  triangle,  O      ,  or  it  may  have  some 

other  form.     We  know  nothing  of  its  shape. 

The  molecule  of  marsh-gas  may  be  represented  by 

HX/H  ^n        XH  ? 

C       ,     H— C— H  ,     C  <**  ,     as  well  as  by   H— C— H . 
H/XH  XH  XH  ^_ 

What  the  formula  docs  mean  to  teach  is,  that  all  the  atoms 
of  hydrogen  are  bound  by  chemical  attraction  to  the  single 
atom  of  carbon,  and  not  to  one  another. 

The  chemist  studies  the  grouping  of  the  atoms  in  the  mole- 
cules, as  the  astronomer  studies  the  grouping  of  the  planets 
and  the  stars  in  cosmic  systems,  and  represents  the  resuits  in 
these  constitutional  formulas. 


58  CHEMISTRY. 

48.  Variable  Quantivaleiice.  —  The  quantivalence  of  an 
atom  is  not  always  the  same.  In  different  compounds  the 
same  atom  may  have  different  values.  For  example,  in  the 

HX/H 
molecule  of  ammonia,      N       ,  nitrogen  is  a  trivalent  atom, 

H 
but   in   a   molecule  of   ammonium  chloride,   N  H4  Cl,  it  is 

H 

H\| 
pentivalent,       N  —  Cl.     Its  value  is  increased  from  3  to  5. 


Whenever  the  quantivalence  of  an  atom  changes,  it  changes 
by  two  units,  as  in  the  example  just  given.  If  the  quantiv- 
alence of  an  atom  is  even  at  one  time,  it  is  always  even.  If  the 
quantivalence  of  an  atom  is  odd  in  one  compound,  it  is  odd 
in  all  compounds.  Hence  the  elements  are  divided  into  two 
classes  ;  one  class  containing  all  those  whose  quantivalence  is 
represented  by  an  even  number,  and  the  other  class  containing 
all  those  whose  quantivalence  is  represented  by  an  odd  num- 
ber. The  members  of  the  first  class  are  called  ARTIADS,  and 
those  of  the  second  are  called  PERISSADS.  An  artiad  may  have 
a  value  represented  by  any  even  number,  as  2,  4,  6,  or  8,  and  a 
perissad  may  have  a  value  represented  by  any  odd  number, 
as  1,  3,  5,  or  7. 

REVIEW. 
L—  SUMMARY   OP  PRINCIPLES. 

49.  An  element  is  a  substance  which  has  never  yet  been 
decomposed. 

There  are  sixty-four  elements  whose  existence  is  at  present 
well  established. 

The  elements  are,  for  convenience  of  study,  divided  into 
two  classes,  metals  and  non-metals. 

The  quantivaleuce  of  an  element  is  the  chemical  value  of 
its  atom,  measured  by  the  number  of  hydrogen  atoms,  or 
their  equivalent,  which  it  can  hold  in  combination. 


CHEMISTRY.  59 

A  univalent  element  is  one  whose  atom  is  equivalent  to  one 
atom  of  hydrogen. 

A  bivalent  element  is  one  whose  atom  is  equivalent  to  two 
atoms  of  hydrogen. 

A  trivalent  element  is  one  whose  atom  is  equivalent  to 
three  atoms  of  hydrogen. 

A  quadrivalent  element  is  one  whose  atom  is  equivalent 
to  four  atoms  of  hydrogen. 

Among  the  non-metals  we  find  no  elements  whose  quantiv- 
alence  is  not  one  or  another  of  these  four  values.  Hence 
the  non-metals  are  placed  in  four  groups  :  the  Univalent,  the 
Bivalent,  the  Trivalent,  and  the  Quadrivalent. 

The  quantivalence  of  an  element  is  represented  to  the  eye 
sometimes  by  a  Roman  numeral,  sometimes  by  primes,  some- 
times by  dashes  attached  to  its  symbol. 

The  quantivalence  of  an  element  is  not  always  -  the  same  : 
it  varies,  however,  only  by  the  addition  or  subtraction  of  two 
units. 

The  formula  for  a  compound  is  a  combination  of  the 
symbols  of  its  elements  to  represent  the  composition  of  a 
molecule. 

A  formula  which  shows  nothing  but  what  is  actually  known 
by  experiment,  the  names  and  proportions  of  the  elements, 
is  an  EMPIRICAL  FORMULA. 

A  formula  which  represents  any  theory  in  regard  to  the 
arrangement  of  the  atoms  in  the  molecule  is  a  RATIONAL 
FORMULA. 

A  formula  which  represents  the  quantivalence  of  the 
atoms,  and  shows  how  the  atoms  are  grouped  in  the  molecule, 
is  a  CONSTITUTIONAL  FORMULA. 

II.— EXERCISES. 

Define  element.  How  many  elements  are  at  present 
recognized?  Are  they  known  to  be  absolutely  simple  sub- 
stances ?  Into  what  classes  are  they  usually  divided  ? 

What  relation  gives  a  better  classification  ?    Illustrate  the 


60  CHEMISTRY. 

equivalence  of  Cl,  O,  N,  and  C  atoms.  Define  the  terms 
univalent,  bivalent,  trivalent,  and  quadrivalent.  Define 
quanti  valence. 

How  is  the  quantivalence  of  an  atom  represented  ?    What 

I 

do  F",  Br',  S",  N  =  ,  -O-,  and-C-  represent? 

I 

What  is  a  graphic  formula?  Write  the  graphic  formula 
for  water,  for  hydrochloric  acid,  for  ammonia,  and  for  marsh- 
gas. 

When  is  a  molecule  said  to  be  saturated?  Unsaturated? 
Write  the  graphic  formula  for  cyanogen.  What  is  the 
quantivalence  of  cyanogen?  Describe  the  quantivalence  of 
any  molecule. 

What  is  a  constitutional  formula?  What  caution  are  we 
to  observe  in  the  use  of  constitutional  formulas  ? 

What  is  an  empirical  formula?  What  is  a  rational 
formula  ? 

SECTION  II. 

HYDROGEN. 

50.  Preparation.  —  Pure  water  consists  of  hydrogen  and 

oxygen,  and  there  are  many 
ways  in  which  the  hydrogen 
may  be  obtained  from  it. 
Many  of  the  metals  have 
power  to  take  the  oxygen 
alone  from  water.  If  a 
piece  of  sodium  be  dropped 
upon  water,  it  melts  into  a 
globule,  floats,  and  runs 
briskly  around  over  the  sur- 
face, taking  the  oxygen  to 
itself,  and  letting  the  hydro- 
gen go  free.  If  the  sodium  be  confined  in  a  net  of  wire- 


CHEMISTRY. 


61 


gauze,  it  may  be  brought  under  the  mouth  of  a  test-tube 
previously  filled  with  water.  (Fig.  22.)  The  hydrogen  will 
then  be  collected  in  the  tube. 

A  more  Practical  Way.  —  Into  a  bottle,  B,  Fig.  23,  are 
put  some  fragments  of  zinc.  Through  the  well-fitting  cork 
pass  two  tubes,  one  a  funnel-shaped  tube  reaching  down  into 
the  bottle,  the  other  a  bent  tube  reaching  over  to  the  cistern 
of  water.  If  now  a  mixture  of  water  and  sulphuric  acid  is 
poured  through  the  funnel  until  the  lower  end  of  its  tube 
is  covered,  hydrogen  will  flow  rapidly  through  the  bent  tube, 


Fig.  23. 

and  may  be  collected  in  jars  upon  the  shelf  of  the  cistern. 
None  should  be  collected,  however,  until  all  the  air  in  the 
apparatus  has  been  driven  out. 

Explanation.  —  The  molecule  of  sulphuric  acid  contains 
two  atoms  of  hydrogen,  one  of  sulphur,  and  four  of  oxygen. 
An  atom  of  zinc  takes  the  place  of  the  two  atoms  of  hydrogen  : 
they  are  driven  away,  while  a  new  molecule  containing  the 
atom  of  zinc  and  those  of  sulphur  and  oxygen  is  formed. 
This  new  molecule  is  zinc  sulphate. 

51.  Reactions. — We  may  represent  this  chemical  change 
to  the  eye  by  formulas  and  algebraic  signs.  Thus  :  — 


62  CHEMISTRY. 

H2  S  O4      +      Zn      =      Zn  S  O4      +      H2. 
Sulph.  acid.  Zinc.  Zinc  sulphate.        Hydrogen. 

The  formulas  for  the  substances  which  were  put  together 
in  the  experiment  are  joined  by  the  sign  of  addition  in  this 
expression,  and  made  the  first  member  of  an  equation  ;  while 
the  new  substances  made  by  the  chemical  action  are  repre- 
sented by  their  formulas  in  the  second  member. 

Chemical  changes  are  very  generally  called  REACTIONS,  and 
are  represented  by  chemical  equations  like  the  one  above. 

Reaction  of  Sodium  and  Water.  —  For  another  exam- 
ple let  us  write  the  reaction  when  hydrogen  is  obtained  by  the 
action  of  sodium.  In  the  experiment  we  put  the  metal  in 
contact  with  water ;  let  us  add  their  formulas  for  the  first 
member  of  our  equation,  and  the  formulas  for  the  substances 
produced  for  the  second. 

H20      +      Na      =      NaHO      +      H. 

Water.  Sodium.        Sodium  Hydrate.     Hydrogen. 

This  equation  shows  us  that  one  atom  of  sodium  takes  the 
place  of  one  atom  of  hydrogen  in  the  molecule  of  water,  and 
produces  one  molecule  of  sodium  hydrate,  and  sets  free  one 
atom  of  hydrogen. 

No  Loss  nor  Gain.  —  Not  an  atom  is  lost,  nor  an  atom 
gained,  in  these  exchanges.  The  second  member  must  show 
the  same  number  of  atoms  of  every  element  found  in  the 
first,  but  differently  arranged  to  make  the  formulas  of  the  new 
compounds.  The  precision  of  exchanges  is,  beyond  com- 
parison, perfect.  To  illustrate  this,  let  us  write  the  same 
equation  with  the  combining  weights  of  the  elements  (see 
table,  p.  53). 

H2  0  +  Na  =         Na  H  0         +  H. 

(2  X  1  +  16)  +  23  =  (23  +  l  +  16)  +  1. 

18  +  23  =  40  -f  1. 

The  two  members  of  this  equation  are  exactly  equal. 


CHEMISTRY. 


63 


This  symbolic  language  of  chemistry  is  of  the  greatest 
value.  It  shows,  at  a  glance,  an  amount  oi*  information 
which,  if  spread  out  in  ordinary  language,  would  often  be 
tedious  or  obscure,  and  reveals  relations  which  in  the  ordi- 
nary language  would  be  unseen. 

The  equation  above  tells  us  that  every  eighteen  grams  of 
water  will  require  exactly  twenty-three  grams  of  sodium  to 
completely  decompose  it,  and  that  exactly  forty  grams  of 
sodium  hydrate  will  be  produced,  and  just  one  gram  of  hy- 
drogen will  be  set  free. 


Fig.  24. 

Reaction  of  Zinc  and  Hydrochloric  Acid.  —  When 
we  use  zinc  and  hydrochloric  acid  as  we  may  in  the  hydrogen 
generator  (Fig.  24) ,  the  reaction  may  be  written 

Zn  +  2HC1  =  ZnCl2  +  H2, 
65   +      73       =136+2; 

which  shows  at  a  glance  that  in  order  to  obtain  two  grams  of 
hydrogen  we  must  use  sixty-five  grams  of  zinc  and  seventy- 
three  of  hydrochloric  acid. 

52.  Physical  Properties.  —  Hydrogen  is  a  colorless 
gas,  and  when  pure  has  neither  taste  nor  odor.  It  is  the 


64 


CHEMISTRY. 


lightest  of  known  substances  ;  its  specific  gravity  is  only 
.0692  (air=l).  It  is  eleven  thousand  times  lighter  than 
water. 

Let  us  take  two  small  glass  vessels,  and  fill  one  with  hydro- 
gen, the  other  with  air.  Then  suppose  we  bring  their  mouths 
together  closely,  so  that  the  one  containing  hydrogen  shall  be 

above  the  other  (Fig.  25). 
Next  turn  them  quickly  over, 
to  bring  the  air-vessel  to  the 
top.  A  moment  afterward 
we  may  remove  the  lower  jar, 
and  then  touch  the  mouth  of 
the  upper  one  with  a  lighted 
match  :  a  sharp  explosion  tells 
us  that  the  hydrogen  is  there. 
It  has  risen  through  the  air 
to  the  top,  just  as  oil  will  rise 
through  water  to  its  surface. 
Soap-bubbles  blown  with 
cold  air  will  fall  to  the  floor, 
but  if  blown  with  hydrogen  they  will  rise  quickly  to  the  ceil- 
ing (Fig.  26). 

This  gas  is  slightly  soluble  in  water,  one  hundred  cubic 
inches  of  which  will  absorb  one  and  a  half  of  hydrogen. 

Hydrogen  is  capable  of  being  absorbed  by  many  metals 
when  heated  to  temperatures  more  or  less  elevated.  The 
most  remarkable  absorption  is  by  the  metal  palladium,  which, 
at  ordinary  temperatures,  will  take  up  more  than  nine  hun- 
dred times  its  own  volume.  Such  absorption  of  gases  by 
metals  is  called  OCCLUSION. 

(Hydrogen,  by  intense  cold  and  enormous  pressure,  may  be 
reduced  to  the  liquid  form.  This  was  first  done  by  two 
experimenters,  M.  Cailletet  and  M.  Pictet,  working  inde- 
pendently, but  succeeding  at  the  same  time,  both  in  Decem- 
ber, 1877.  M.  Cailletet  brought  the  gas  under  a  pressure  of 
nearly  three  hundred  atmospheres,  and  then  suddenly  released 


Pig.  25. 


CHEMISTRY.  65 

it.  By  the  sudden  expansion  of  a  portion  of  the  gas  the 
temperature  of  the  rest  was  enormously  reduced,  and  the 
hydrogen  took  the  form  of  mist. 

M.  Pictet  subjected  the  gas  to  a  temperature  of  —140  C., 
and  a  pressure  of  six  hundred  and  fifty  atmospheres.  On 
opening  a  valve  the  hydrogen  came  out  in  a  jet  of  steel-blue 
color.  But  after  a  little  while,  on  opening  the  valve  a  second 
time,  and  although  the  pressure  was  still  three  hundred  arid 


Fig.  26. 

fifteen  atmospheres,  no  hydrogen  came  out.  The  fact  that 
no  gas  issued  when  under  such  pressure  showed  that  the 
hydrogen  was  not  only  liquefied  but  actually  reduced  to  the 
solid  form  :  it  was  frozen. 

53.  Chemical  Properties.  —  Hydrogen  is  a  combustible 
gas.  If  a  small  jar,  filled  with  it,  is  carefully  lifted  from  the 
cistern,  and  a  lighted  taper  is  quickly  pushed  up  into  it  (Fig. 
27),  the  gas  takes  fire  with  a  slight  explosion. 


66 


CHEMISTRY. 


We  may  study  the  flame  by  means  of  the  apparatus  shown 
in  Fig.  28.     The  hydrogen   generator  is   connected  with  a 

second  bottle  by  a  bent 
tube  reaching  down 
nearly  to  the  bottom. 
This  bottle  contains 
some  water,  and  is  pro- 
vided with  a  tall  tube 
whose  upper  end  is 
drawn  to  a  small  open- 
ing. Let  the  acid  be 
poured  through  the  fun- 
nel upon  the  zinc,  until 
a  rapid  evolution  of  the 
gas  is  produced,  and 
wait  until  the  gas  has 
driven  the  air  completely 
from  the  apparatus.  Then  touch  the  jet  of  escaping  hy- 
drogen with  a  match-flame  :  it  will  take  fire,  and  continue  to 
burn  as  long  as  the  gas  is  supplied. 

The  flame  of  pure  hydro- 
gen yields  almost  no  light, 
but  its  heat  is  intense.  One 
gram  of  hydrogen  will  yield 
heat  enough  to  raise  34,462 
grams  of  water  from  0°  to 


Pig.  27. 


The  mixture  of  hydrogen 
with  air  is  explosive.  When 
the  mixture  is  made  with 
oxygen,  in  the  proportions 
of  two  volumes  hydrogen  to 
one  volume  oxygen,  the  ex- 
plosion is  deafening.  If  it 
takes  place  in  free  air,  it  is 
uot  dangerous ;  but,  if  the  mixture  is  confined  in  a  tight 


Fig.  28. 


CHEMISTRY.  67 

bottle,  the  fragments  of  the  bottle  will  be  driven  with  vio- 
lence as  by  a  charge  of  gunpowder. 

The  combustibility  and  the  explosibility  of  hydrogen  are 
due  to  the  strong  chemical  attraction  between  it  and  oxygen. 
It  also  enters  into  combination  with  the  other  non-metals 
with  the  exception  of  boron  ;  but  its  compounds  with  the 
metals  are  rare.  By  some  chemists  it  is  regarded  as  itself  a 
metal,  and  has  been  called  HYDROGENIUM.  This  view  is 
based  upon  the  general  resemblance  of  the  chemical  actions 
of  hydrogen  and  the  metals. 

The  molecule  of  hydrogen  is  supposed  to  contain  two 
atoms.  Its  symbol  is  H,  which  represents  one  atom,  but  its 
molecule  is  represented  by  H — H,  or  H2. 

54.  Occurrence.  —  Hydrogen    rarely    occurs    in    nature 
free  ;  it  has  been  found  among  the  gases  given  off  in  volcanic 
eruptions  ;  but  in  compounds  it  is  a  very  abundant  element. 
One-ninth,  by  weight,  of  all  the  water  of  the  globe,  is  hydro- 
gen ;  and  besides  this  it  is  an  important  element  in  all  animal 
and  vegetable  bodies. 

55.  Hydrogen  as  a  Standard.  —  This  element  has  been 
adopted  as  the  standard  of  atomic  weight,  of  equivalence,  of 
density  of  gases,  and  of  molecular  weight. 

The  weight  of  its  atom  is    1  =  unit  of  atomic  and  molecular  weight. 

Its  atom  value  or  quan- 

tivalence  is  .  .  1  =  "  quantivalence. 

The  weight  of  a  unit  vol- 
ume is  .  .  .  1  =  "  density  or  specific  gravity. 

Its  molecular  weight  =  2  atomic  weights  is         ...       2 

The  weight  of  1  liter  is 0.08936  gram. 

REVIEW. 
I. —SUMMARY  OP  PRINCIPLES. 

56.  Hydrogen  may  be  obtained  from  water  by  the  action 
of  sodium  or  of  potassium  at  ordinary  temperature. 

It  may  also  be  obtained  from  water  by  iron  and  some  other 
metals  at  a  red  heat. 


68  CHEMISTRY. 

It  may  also  be  obtained  from  water  by  electrolysis. 

It  is  usually  obtained  by  the  action  of  zinc  upon  dilute 
sulphuric  or  hydrochloric  acid. 

Hydrogen  is  the  lightest  known  substance  :  it  is  14.4  times 
lighter  than  atmospheric  air. 

With  air  it  is  combustible  and  explosive.  It  will  not 
support  combustion  nor  animal  life. 

Its  symbol  is  H,  and  its  atomic  weight  is  1.  Its  molecule 
is  represented  by  H — H,  and  its  molecular  weight  is  2.  Its 
density  is  1,  and  its  quantivalence  is  1. 

Chemical  changes  are  called  reactions.  Reactions  are 
written  in  the  form  of  equations.  The  formulas  of  the  sub- 
stances entering  into  the  action  are  connected  by  the  sign  of 
addition  to  form  the  first  member,  while  the  formulas  of  the 
substances  produced  by  the  action,  joined  by  the  same  sign, 
form  the  second  member,  of  the  equation. 

The  molecular  weights  of  the  various  substances  repre- 
sented in  the  equation  show  the  relative  quantities  of  them 
which  take  part  in  the  reaction. 

II.— EXERCISES. 

Describe  the  preparation  of  hydrogen  by  the  use  of 
sodium.  By  the  use  of  zinc.  Give  the  explanation. 

What  is  a  chemical  reaction?  How  are  reactions  writ- 
ten? Write  the  reaction  of  sodium  and  water  in  the 
preparation  of  hydrogen.  What  does  the  equation  show? 
Write  the  equation  with  the  numerical  values  of  the  sub- 
stances. What  does  this  numerical  equation  show? 

In  the  equation  we  find  that  eighteen  grams  of  water  will 
yield  just  one  gram  of  hydrogen :  then  how  much  water 
would  be  needed  to  yield  twenty  grams  of  hydrogen  ? 

How  much  sodium  would  be  needed  with  it? 

How  much  sodium  hydrate  would  be  formed? 

How  much  water  would  be  required  to  yield  seventy-five 
grams  of  hydrogen  ?  Ans.  1,350  grams. 


CHEMISTKY.  69 

How  many  liters  of  hydrogen  will  be  liberated  from  one 
hundred  grams  of  water  by  sodium  ? 

1 00 

Ans,  100  grams  H2O  yield  -  -  of  1  gram  H  =  5.555 4-. 

18 

A  liter  of  H  weighs  0.08936  gram  ;  hence  — - — —  =  the 

0.08936 

number  of  liters  =  62.16  +  . 

Write  the  reaction  of  zinc  and  hydrochloric  acid.  Change 
it  to  a  numerical  equation. 

How  much  zinc  must  be  used  to  prepare  seventy-five  grams 
of  hydrogen? 

How  many  liters  of  hydrogen  will  be  set  free  by  using  one 
hundred  grams  of  zinc? 

How  much  hydrochloric  acid  will  be  required  to  liberate 
one  hundred  liters  of  hydrogen  ? 

Ans.  0.08936  x  100  =  8.936  grams,  the  weight  of  100 
liters  H  ;  to  liberate  2  grams  H,  requires  73  of  H  Cl  (see 

Q   O  Q  R. 

reaction)  ;  hence  — X  73  =  326.164  grams  HC1  will 

be  required  for  100  liters  of  H. 

How  many  grams  of  H2  S  O4  must  be  decomposed  by  zinc 
to  yield  one  hundred  liters  of  H  ? 

Give  the  physical  properties  of  hydrogen.  What  is 
occlusion  ? 

Why  is  hydrogen  combustible  ?  How  much  heat  is  evolved 
by  the  combustion  of  one  gram  of  hydrogen? 

Where  is  hydrogen  found  in  nature?  Give  the  symbol 
of  hydrogen.  Atomic  weight.  Quantivalence.  Density. 
Molecular  weight.  How  is  the  molecule  of  hydrogen  repre- 
sented in  symbols? 


70 


CHEMISTEY. 


SECTION  III. 

THE  UNIVALENT  NON-METALS. 
I.  —  CHLORINE. 

57.  Preparation     from     Hydrochloric     Acid.  —  The 

chlorine  in  hydrochloric  acid  may  be  set  free  by  the  action 

of  manganese  diox- 
For  this  pur- 
the  acid,  with 


ide. 
pose 

about  one-third  of 
its  weight  of  the  di- 
oxide, is  put  into  a 
large  flask  (Fig.  29), 
provided  with  a  tight 
cork  and  suitable 
tubes  as  represented 
in  the  cut.  By  heat- 
ing the  mixture  gen- 
tly, the  chlorine  is 
given  off  in  abun- 
dance ;  passes  over 
through  the  tube  to 

the  bottom  of  the  jar,  A,  in  which  it  gradually  rises,  until 

the  jar  is  filled. 

The  reaction  is  as  follows  :  — 

Mn  O2  +  4  H  Cl  =  2  H2  O  +  Mn  C12  +  2  Cl. 

This  equation  is  read  in  this  way :  One  molecule  of 
manganese  dioxide  with  four  molecules  of  hydrochloric  acid, 
yield  two  molecules  of  water,  one  of  manganese  dichloride, 
and  two  atoms  (one  molecule)  of  chlorine. 

The  oxygen  of  the  dioxide,  combining  with  the  hydrogen 
of  the  acid,  forms  water  ;  while  a  part  of  the  chlorine,  taking 


Pig.  29. 


y"V  f%TP 

the  manganese,  forms  manganic  chloride,  and  the  rest  of  the 
gas  is  set  free. 

Preparation  lyy  Use  of  Common  Salt.  —  In  place  of 
hydrochloric  acid  we  may  use  sodium  chloride  and  sulphuric 
acid :  these  with  the  manganese  dioxide,  gently  heated, 
evolve  the  gas  abundantly.  The  following  equation  shows 
the  chemical  changes  which  occur  :  — 

2  Na  Cl  +  3H2  S  O4  +  Mn  O2  =  2  Na H S  O4+  Mn  S  O4+2  Cl  +  2  H2  O. 


Sodium 
Chloride. 


Sulphuric 
Acid. 


Manga-  Hydro-  Manga- 

nese Sodium  nese       Chlorine.    Water. 

Dioxide.         Sulphate.  Sulphate. 


!jjig^  '^|W^i_ 

xr^. !  .      '  I  J 


Fig.  30. 

To  Obtain  the  Gas  Pure  and  Dry.  —  To  purify  and 
dry  the  gas,  obtained  by  either  of  these  methods,  it  is  passed 
from  the  flask  first  through  water  contained  in  a  wash- 
bottle,  —  the  three-necked  bottle  in  Fig.  30,  —  and  then 
through  a  vessel  —  the  tall  jar  in  the  figure  —  containing 


72  CHEMISTRY. 

calcium  chloride.  The  water  washes  out  the  impurities,  and 
the  chloride  absorbs  the  moisture.  The  pure,  dry  chlorine 
may  then  be  collected  in  bottles  or  jars. 

58.  Physical    Properties.  —  Chlorine    is    a   transparent 
gas,    having   a   greenish-yellow   color   and    a    characteristic 
suffocating  smell.     When  inhaled,  it  powerfully  irritates  the 
air-passages,  and  produces  coughing,  even  when  mixed  with 
large   portions   of    air.      If   breathed   pure   it   even   causes 
death. 

Chlorine  is  nearly  two  and  a  half  (2.45)  times  heavier 
than  an  equal  volume  of  air.  Its  density,  hydrogen  being 
the  standard,  is  35.37. 

Chlorine  is  very  soluble  in  cold  water.  Water,  at  ordinary 
temperature,  dissolves  about  twice  its  own  bulk.  It  dissolves 
less  and  less  as  the  temperature  rises,  until  at  100°  C.  it  dis- 
solves none. 

The  solution  of  chlorine  is  useful  in  the  laboratory  ;  and  it 
is  prepared  by  passing  the  gas  from  the  generator  through 
water,  as  shown  in  Fig.  31.  The  gas  is  washed  in  the  small 
bottle,  and  dissolved  in  those  which  follow. 
r  Under  a  pressure  of  four  atmospheres,  chlorine  becomes  a 
lyellow  liquid  at  ordinary  temperature.  If  cooled  to  —34°  C., 
the  same  effect  is  produced  without  any  extra  pressure. 

59.  Chemical   Character. —  Chlorine    combines    readily 
with  hydrogen.     The  application  of  either  heat  or  light  will 
cause  them  to  unite.     When  a  mixture  of  the  two  is  placed 
in  the  direct  rays  of  the  sun,  the  combination  is  rapid,  some- 
times with  explosion.     Diffuse  light  causes  the  combination 
gradually ;  while,  if  mixed  and  kept  in  the  dark,  no  chemical 
action  takes  place. 

So  strong  is  the  chemical  force,  or  affinity,  between  these 
elements,  that  chlorine  will  decompose  many  compounds  of 
hydrogen.  An  instructive  experiment  illustrates  this.  A 
lighted  wax-taper,  plunged  into  a  jar  of  chlorine,  is  extin- 
guished ;  but,  curiously  enough,  it  is  at  once  relighted,  burn- 


CHEMISTRY. 


73 


ing  afterward  with  a  dark  red  flame,  and  giving  off  a  dense 
black  smoke.  The  explanation  is  this :  the  white  flame  in 
the  air  is  due  to  the  action  of  oxygen  ;  and  since  there  is 
none  of  this  element  in  the  jar,  the  flame  dies.  But  the  wax 
contains  hydrogen  ;  and  the  chlorine  decomposes  the  wax, 
and  combines  with  this  element  so  vigorously  as  to  produce 
a  dull  red  flame. 


Fig.  31. 

Application  of  this  Affinity.  —  Chlorine  is  largely  used 
in  the  arts  of  bleaching  and  disinfecting.  But  dry  chlorine 
will  not  bleach :  it  must  be  moist.  Its  power  to  destroy 
colors  and  odors  is  due  to  its  attraction  for  hydrogen. 

In  bleaching,  the  chlorine  decomposes  the  water  present, 
and  combines  with  its  hydrogen.  The  oxygen  of  the  water 


74 


CHEMISTRY. 


then  attacks  the  coloring  matter,  decomposing  it  and  destroy- 
ing the  color. 

Chlorine  and  the  Metals.  —  Chlorine  combines,  also, 
with  most  metals  readily.  Powdered  antimony  sprinkled 

into  a  bottle  of  chlo- 
rine takes  fire  (Fig. 
32),  and  falls  to  the 
bottom  in  a  shower 
of  sparks.  Metals 
which,  like  gold,  re- 
sist the  action  of  ox- 
ygen and  the  acids, 
are  attacked  by  chlo- 
rine. Neither  nitric 
acid  nor  hydrochloric 
acid  alone  will  act 
upon  gold,  but  when 
mixed  they  form 
what  is  called  aqua- 
regia,  in  which  there 
is  free  chlorine ;  by 
this  mixture  gold  tri- 
chloride is  speedily 
formed. 

60.  Occurrence.  —  Chlorine  is  not  found  free  in  nature, 
but  in  combination  it  is  one  of  the  most  abundant  ele- 
ments. Sodium  chloride  (common  salt,  NaCl)  is  distributed 
throughout  the  air,  the  soil,  the  rocks,  and  the  sea.  More 

than  half  I — '—]  the  weight  of  this  substance  is  chlorine; 


Fig.  32. 


and  calculating  from  the  amount  of  salt  in  sea-water,  we 
may  find  that  something  more  than  five  gallons  of  this  gas 
is  contained  in  the  salt  of  one  gallon  of  sea- water.  Other 
chlorides  exist  in  the  water  of  the  sea :  potassium  and  mag- 
nesium chlorides  are  the  most  abundant.  Chlorides  are 
found  also  in  th<i  bodies  of  plants  and  animals. 


CHEMISTRY.  75 

II.  —  BROMINE,  IODINE,  AND  FLUORINE. 

61.  Bromine.  —  Bromine   is   found   in    small    quantities 
combined  with  metals  in  the  waters  of  the  sea.     It  is  a  dark 
brown-red  liquid,  having  a  strong   affinity  for  hydrogen   and 
the   metals.     Its   compounds   are   used   to   some   extent   in 
medicine,  and  quite  largely  in  photography. 

62.  Iodine.  —  Iodine,  like  chlorine  and  bromine,   is  not 
found  free  in  nature,  but  combined  with  metals  it  is  found 
in  sea-water,  in  sea-plants,  and  in  some  mineral  springs. 

It  is  a  blue-black  crystalline  solid,  very  volatile,  giving  off 
a  superb  violet-colored  vapor  when  warmed.  It  has  a  strong 
affinity  for  hydrogen  and  the  metals.  Its  compounds  are 
used  in  photography,  and  are  highly  prized  in  medicine. 

63.  Fluorine.  —  Fluorine  is  found  combined  with  metals 
in   certain   minerals  —  fluor-spar    (calcium  fluoride,  Ca  F12) 
being  the  most  common.     It  is  obtained  free  only  with  the 
greatest  difficulty,  and  on  this  account  its  physical  properties 
are  imperfectly  known.     It  seems  to  be  a  gas,   having   a 
violent  affinity  for  hydrogen,  for  the  metals,  and,  indeed,  for 
many  other  elements. 

III.  —  THE  GROUP. 

64.  Comparison     of     their    Physical    Properties. — 

Leaving  fluorine  out  of  the  account,  we  notice  that  chlorine 
is  a  gas  at  ordinary  temperature,  bromine  a  liquid,  and 
iodineja"solid.  At  a  little  higher  temperature  all  three  are 
gaseous.  In  the  colors  of  these  gases  we  notice  a  curious 
gradation.  That  of  bromine  represents  one  end  of  the 
spectrum,  dark-red ;  that  of  chlorine  represents  the  middle 
part,  greenish-yellow ;  and  that  of  iodine  represents  the 
Other  end,  a  beautiful  violet. 

Comparison  of  their  Chemical  Properties.  —  These 
four  elements  closely  resemble  each  other  in  their  chemical 
properties.  They  combine  with  the  same  substances,  and 


76  CHEMISTRY. 

generally  in  the  same  proportions.  For  hydrogen  and  the 
metals  they  all  have  strong  attraction  ;  with  oxygen  they  (with 
the  possible  exception  of  fluorine)  unite,  although  with  a 
feeble  force ;  with  nitrogen  they  form  explosive  compounds. 
They  are  all  univalent,  and  the  single  compound  which  each 
one  forms  with  hydrogen  is  an  acid. 

The  following  formulas  illustrate  the  analogous  composi- 
tion of  the  hydrogen  compounds  of  these  elements  :  — 

H  Cl  .  .  .  Hydrochloric  acid. 

H  Br  .  .  .  Hydrobromic  acid. 

HI  .         .  .  .  Hydriodic  acid. 

H  F  .         .  .  .  Hydrofluoric  acid. 

IV.  —  HYDROCHLORIC  ACID. 

65.  Hydrochloric  Acid  is  a  Gas.  —  The  hydrochloric 
acid  found  in  commerce  is  a  liquid,  but  a  simple  experiment 
will  show  that  this  liquid  is  the  solution  of  a  gas  in  water. 


Fig.  33. 

Some  of  the  liquid  is  put  into  a  flask  (Fig.  33),  and  heated : 
a  colorless  gas  is  by  this  means  driven  over  through  the  bent 
tube,  and,  being  dried  while  going  through  sulphuric  acid  in 
the  bottle  B,  finally  enters  a  jar,  previously  filled  with  mer- 


CHEMISTRY.  77 

cury,  and  inverted  over  a  small  cistern  of  the  same  fluid. 
If,  when  the  jar  is  full  of  gas,  it  be  taken  from  the  mercury 
and  its  open  mouth  inserted  in  water,  the  gas  will  be  dis- 
solved, the  water  rising  into  the  jar  at  the  same  time  with 
surprising  swiftness.  Now,  the  solution  thus  obtained  is 
found  to  be  weak  hydrochloric  acid,  and  we  hence  learn  that 
the  real  acid  is  a  gas. 


InmlliililllM 

Fig.  34. 

66.  Preparation.  —  For  some  purposes  the  gas  may  be 
obtained  in  small  quantity,  by  the  process  just  described. 

It  may,  however,  be  made  by  the  reaction  of  common  salt 
with  sulphuric  acid. 

For  this  purpose  six  parts  by  weight  of  salt  are  put  into  a 


78 


CHEMISTRY. 


large  flask,  and  eleven  parts  of  strong  acid  are  slowly  poured 
through  a  funnel-tube  upon  it.  The  gas  is  rapidly  set  free, 
and  is  purified  by  passing  through  a  little  water  in  a  wash- 
bottle  ;  after  which  it  may  be  collected  over  mercury,  as 
shown  in  Fig.  34,  or  by  displacement  like  chlorine,  or  it  may 
be  dissolved  by  passing  it  into  water. 

The  Reaction.  —  The  salt  furnishes  the  chlorine,  and  the 
sulphuric  acid  furnishes  the  hydrogen,  to  form  the  hydro- 
chloric acid.  The  chemical  change  is  as  follows  :  — 


H2S04  .=  NaHS04  +  H  Cl. 

A  molecule  of  sodium  chloride,  with  a  molecule  of  sul- 
phuric acid,  yields  a  molecule  of  hydro-sodium  sulphate  and 
one  molecule  of  hydrochloric  acid. 


Fig.  35. 

67.  Physical  Properties.  —  Hydrochloric  acid  is  a  color- 
less gas,  a  little  heavier  than  air,  and  18.2  times  heavier  than 
hydrogen. 

One  of  its  most  remarkable  properties  is  its  solubility  in 
water.;  and  it  is  this  solution  which  is  found  in  commerce 


CHEMISTRY.  79 

and  used  in  the  laboratory,  as  hydrochloric  acid.  The  great 
solubility  of  this  gas  may  be  demonstrated  by  experiment 
with  apparatus  shown  in  Fig.  35.  Some  commercial  acid  is 
heated  in  the  small  flask.  The  acid  gas  is  rapidly  evolved. 
It  passes  into  the  upper  bottle,  and  drives  the  air  before  it, 
out  through  the  side  tube,  which  reaches  over  to  the  surface 
of  water  in  a  beaker.  When  the  air  has  been  all  driven  out, 
this  side  tube  is  closed  by  a  spring-clamp.  The  gas  then 
passes  down  the  vertical  tube,  which  reaches  from  the  upper 
bottle  to  the  bottom  of  another  below  containing  water  colored 
blue  with  litmus.  The  flame  is  then  withdrawn  from  the 
flask,  and  the  other  clamp  immediately  closed.  At  this  mo- 
ment the  upper  bottle  and  the  vertical  tube  are  filled  with 
the  acid  gas.  The  water  then  quickly  absorbs  the  gas,  and 
ascends  the  vertical  tube.  It  enters  the  upper  bottle  in  the 
form  of  a  fountain,  and  continues  to  rise  as  long  as  any  gas 
remains  to  be  absorbed.  At  15°  C.,  water  dissolves  four  hun- 
dred and  fifty  times  its  own  volume  of  hydrochloric  gas.  On 
contact  with  air  the  colorless  gas  takes  moisture,  and  yields 
dense  white  fumes. 

68.  Chemical  Properties.  —  Hydrochloric  acid  is  an 
energetic  acid.  It  reddens  litmus,  and  it  readily  yields  its 
hydrogen  when  acted  on  by  metals.  For  example  :  — 

HC1        -f-      Na'       =         NaCl       4-        H. 
Acid.  Sodium.        Sodium  Chloride.     Hydrogen. 

2HC1       +      Zn"      =         ZnCl2      +     2H. 
Acid.  Zinc.  Zinc  Chloride.       Hydrogen. 

The  metals  take  the  place  of  the  hydrogen  of  the  acid, 
and  produce  chlorides. 

The  gas  is  wholly  irrespirable.  It  will  neither  burn  nor 
support  combustion. 

The  molecular  weight  of  hydrochloric  acid  is  36.5 
(H  =  1,  01  =  35.5),  and  its  molecular  volume  is  two. 

35  5 
Hence  its  density  is  —^=18.25. 


80  CHEMISTRY. 

69.  Uses.  —  In  the  manufacture  of  many  commercial  prod* 
ucts,  such,  for  example,  as  gelatine,  "  bleaching-powder,'* 
and  many  chemicals,  hydrochloric  acid  is  used  in  very  great 
quantities.     In  the  laboratory  of  the  chemist  it  is  an  indis- 
pensable reagent. 

REVIEW. 
I. —SUMMARY   OF  PRINCIPLES. 

70.  Chlorine  is  obtained  by  gently  heating  a  mixture  of 
hydrochloric  acid  and  manganese  dioxide. 

It  is  a  heavy  greenish-yellow  gas,  with  a  penetrating  and 
characteristic  odor.  It  is  soluble  in  one-half  its  volume  of 
cold  water. 

Its  most  characteristic  attractions  are  for  hydrogen  and  the 
metals.  With  hydrogen  it  combines  in  equal  volumes,  and 
forms  hydrochloric  acid ;  with  the  metals  it  forms  a  large 
class  of  compounds  called  chlorides. 

Its  affinity  for  hydrogen  is  taken  advantage  of  in  the  pro- 
cess of  bleaching  cotton  fabrics.  Only  moist  chlorine  will 
remove  color  or  destroy  bad  odors. 

The  gas  is  not  found  in  nature  free,  but  its  compounds  are 
very  abundant.  The  most  abundant  chloride  is  common 
salt,  —  the  sodium  chloride  (NaCl). 

Chlorine,  Bromine,  Iodine,  and  Fluorine  form  a  well- 
marked  chemical  group.  They  are  all  univalent  elements. 
They  enter  into  combination  with  the  same  elements,  and 
then:  compounds  have  similar  composition. 

Hydrochloric  acid  is  the  only  known  compound  of  chlorine 
and  hydrogen.  It  was  formerly  called  MURIATIC  ACID. 

It  is  manufactured  in  large  quantities  for  many  commercial 
purposes.  Common  salt  and  sulphuric  acid  are  the  materials 
employed.  When  heated  together  they  evolve  large  volumes 
of  the  gas,  which  is  dissolved  in  water  to  constitute  the 
commercial  acid. 

The  commercial  acid  is  usually  highly  colored  yellow  by 


CHEMISTRY.  81 

the   presence   of    organic   impurities.     The   pure   article   is 
perfectly  colorless. 

Hydro-sodium  sulphate  (Na  H  S  04)  or  sodium  sulphate 
(Na2  S  O4)  is  formed  at  the  same  time  with  the  acid :  the 
first,  if  one  molecule  of  salt  to  one  of  sulphuric  acid  are  the 
proportions  used  ;  and  the  second,  if  two  molecules  of  salt 
are  used  to  one  of  the  acid,  thus  :  — 

2NaCl  +  H2S04  =  Na2SO4  +  2HC1. 

This  sodium  sulphate  (Na2  8  O4)  is  used  in  the  manufac- 
ture of  sodium  carbonate.  It  is  the  well-known  Glauber's 
Salts. 

Hydrochloric  acid  changes  many  metals  into  chlorides. 
The  chemical  action  consists  in  the  substitution  of  an  atom 
of  the  metal  for  the  hydrogen,  in  one  or  more  molecules  of 
the  acid. 

The  substitution  will  be  for  hydrogen  in  one  molecule  of 
acid  if  the  metal  is  univalent,  in  two  molecules  of  the  acid 
if  the  metal  is  bivalent,  and  in  three  if  the  metal  is  trivalent. 

These  chlorides  are  all  very  soluble  in  water,  except  three. 
Silver  chloride  (AgCl),  mercurous  chloride  (Hg2Cl2),  and 
lead  chloride  (Pb  C12),  are  the  three  exceptions. 

A  mixture  of  hydrochloric  acid  and  nitric  acid  is  called 
AQUA  REGIA.  Neither  of  these  acids  alone  can  attack  gold, 
but  aqua-regia  quickly  converts  gold  into  a  chloride 
( Au  C13) .  Aqua-regia  owes  this  power  to  dissolve  gold  to 
the  free  chlorine  which  it  contains. 

II.— EXERCISES. 

Describe  the  preparation  of  chlorine. 

Give  the  reaction.  Take  the  needed  atomic  weights  from 
the  table  of  elements,  p.  53.  and  write  the  numerical  equa- 
tion in  the  reaction. 

How  many  grams  of  Cl  may  be  obtained  by  using  fifty 
grams  of  hydrochloric  acid?  Ans.  24.315. 


82  CHEMISTEY. 

How  many  liters  in  this  weight  of  chlorine :  its  density 
being  35.5? 

Ans.  0.08936  x  35.5  =  weight  of  1  liter  of  Cl. 

24.315  grams  ,  ,.,  ~. 

—  =  number  of  liters  of  CL 
weight  of  1  liter 

What  volume  of  chlorine  will  fifty  grams  of  Mn  O2  liberate 
from  H  Cl  when  the  two  are  heated  together  ? 

What  is  the  weight  of  2,500  cubic  centimeters  of  chlorine 
gas? 

What  are  the  physical  properties  of  chlorine  ?  Illustrate 
the  chemical  attraction  of  chlorine  and  hydrogen.  To  what 
useful  purposes  is  this  property  of  chlorine  applied  ?  Explain 
the  bleaching  action  of  chlorine. 

Illustrate  the  chemical  attraction  of  chlorine  and  the 
metals.  What  class  of  compounds  does  chlorine  form? 
What  is  aqua-regia  ? 

In  what  form  is  chlorine  abundant  in  nature  ? 

Give  a  brief  description  of  bromine. 

Give  a  brief  description  of  iodine. 

Give  a  brief  description  of  fluorine. 

Compare  the  physical  properties  of  chlorine,  bromine,  and 
iodine.  Compare  their  chemical  properties.  Give  the 
formulas  and  names  of  their  hydrogen  compounds.  What 
is  the  quantivalence  of  the  members  of  this  group  ? 

What  is  the  liquid  hydrochloric  acid  of  commerce  ?  How 
may  the  gas  itself  be  obtained?  Write  the  reaction  when 
salt  is  used  with  sulphuric  acid. 

What  are  some  of  the  properties  of  this  gas  ? 

Describe  its  solubility. 

What  chemical  change  occurs  when  sodium  and  hydro- 
chloric acid  are  brought  together? 

What  chemical  change  when  zinc  and  hydrochloric  acid 
are  brought  together? 

What  class  of  substances  are  formed  by  the  action  ol 
metals  on  this  acid  ? 

What  are  the  uses  of  this  acid? 


CHEMISTRY. 


SECTION  IV. 

THE  BIVALENT  NON-METALS. 
I.  —  OXYGEN. 

71.  Preparation.  —  Oxygen  may  be  obtained  by  heating 
potassium  chlorate.  This  is  the  best  and  usual  method. 
Potassium  chlorate  is  a  white  solid,  about  39.2  per  cent  of 
its  weight  being  oxygen.  It  gives  up  all  this  oxygen  when 
heated.  For  this  purpose  it  is  finely  powdered,  mixed  with 
about  an  equal  weight  of  black  oxide  of  manganese,  and  put 


Fig.  36. 

into  a  flask,  F  (Fig.  36).  A  bent  tube  reaches  through  tne 
cork  of  the  flask  and  over  into  the  water  of  the  cistern  ;  and 
upon  the  shelf  of  the  cistern  there  stands  an  inverted  jar 
filled  with  water.  Now,  when  the  flask  is  heated,  the 
chlorate  is  decomposed,  and  oxygen,  being  set  free,  passes 
through  the  bent  tube,  and  bubbles  out  of  the  water.  If  the 
end  of  the  tube  is  brought  under  the  mouth  of  the  jar,  the 
oxygen  will  rise  into  the  jar,  which  in  a  little  time  will  be 
filled.  The  reaction  is  as  follows  :  — 


84 


CHEMISTRY. 


KC1O3  =  KC1  +        03. 

Potassium  chlorate  =  Potassium  chloride  +  Oxygen. 
122.6  =  74.6  -f         48. 

The  manganese  dioxide  is  used  in  order  to  obtain  the  gas 
at  a  lower  temperature.  It  takes  no  part  in  the  chemical 
action,  and,  in  the  end,  is  found  mixed  with  the  potassium 
chloride  in  the  flask. 

72.  Its  Physical  Properties.  —  Oxygen  is  a  colorless 
and  transparent  gas  ;  without  odor  or  taste  ;  a  little  heavier 
than  air,  its  specific  gravity  being  1.1056  (air  =  1),  or  16 
when  hydrogen  is  the  unit. 

This  gas  is  slightly  soluble  in  water,  one  hundred  volumes 
of  water  absorbing  about  three  volumes  of  oxygen  at  ordinary 
temperatures. 

s~  When  submitted  to  a  pressure  of  three  hundred  atmos- 
pheres, and  a  cold  of  —140°  C.,  if  the  pressure  be  suddenly 
removed  oxygen  is  reduced  to  the  liquid 
form.      This   liquefaction  was   accom- 
plished by  Pictet  in  December,  1877. 

73.  Its  Chemical  Properties. — A 

lighted  taper  lowered  into  a  jar  of  oxy- 
gen burns  with  surprising  brilliancy. 
A  glowing  spark  upon  the  wick  is  all 
that  is  needed :  the  oxygen  instantly, 
and  with  a  slight  explosion,  kindles  it 
into  a  vivid  flame. 

Into  a  jar  of  oxygen,  hang,  by  means 
of  a  wire,  a  piece  of  charcoal  bark  on 
which  there  is  a  spark  of  fire  (Fig.  37). 
Quickly  the  charcoal  bursts  into  a  beau- 
tiful and  vigorous  combustion.  The 
carbon  combines  with  the  oxygen,  and  produces  carbon  di- 
oxide, thus : — 

C       +       O2       =  C02 

Carbon  +  Oxygen  =  Carbon  dioxide. 


Fig.  37. 


CHEMISTRY. 


85 


Experiments  like  these  illustrate  the  fact  that  bodies  which 
burn  in  air  will  burn  with  greater  vigor  in  oxygen. 

Again  :  let  an  iron  wire  or  a  steel  watch-spring  be  tipped 
with  a  bit  of  wood.  Set  fire  to  the  wood,  and  at  once  plunge 
it  into  a  jar  of  oxygen.  Quickly  the  metal  takes  fire,  and 
burns  (Fig.  38),  the  iron  with  a  steady  and  beautiful  light, 
or  the  steel  with  a  multitude  of  star-like  sparks.  Iron 
sesquioxide  (Fe2  O3)  is  pro- 
duced by  this  chemical  ac- 
tion. Experiments  such  as 
this  illustrate  the  fact  that 
substances  which  do  not  burn 
in  air  may  burn  with  great 
rapidity  in  oxygen. 

This  gas  not  only  supports 
combustion,  it  is  also  neces- 
sary to  the  life  of  animals. 
It  is  in  the  air,  and  animals 
breathe  it ;  it  goes  into  their 
blood,  and  purifies  it.  By 
being  mixed  with  nitrogen, 
its  violent  action  is  toned 
down  so  that  the  most  deli- 
cate organ  may  not  only  withstand  it,  but  be  invigorated  by 
its  presence. 

Oxygen  unites  with  all  other  elements  with  the  exception 
of  fluorine,  and  its  compounds  are  very  numerous  and 
abundant. 

Its  combining  weight  is  16.  Its  molecule  is  supposed 
to  contain  two  atoms  ;  so  that  while  the  symbol  of  oxygen  is 
O,  its  molecule  is  represented  by  O  zz  O  or  O2,  and  its  molec- 
ular weight  is  therefore  32,  and  molecular  volume  2. 

74.  Occurrence.  —  Oxygen  is  the  most  abundant  element 
in  nature :  minerals,  plants,  and  animals  alike  contain  large 
quantities  of  it.  One-fifth  part  of  the  air  by  weight  is 


Pig.  38. 


86 


CHEMISTBY. 


oxygen,  eight-ninths  of  all  the  water  on  the  globe,  and  about 
one-half  of  all  the  solid  rocks.  Besides  this  about  four-fifths 
of  the  weight  of  vegetable  bodies  is  oxygen,  and  about  three- 
fourths  of  that  of  animals.  It  is,  perhaps,  not  too  much  to 
say,  that  one-half  of  all  the  matter  of  the  world,  as  far  as  it 
has  been  examined,  is  oxygen.  And  yet,  when  freed  from 
its  prisons  in  solid  and  liquid  bodies,  oxygen  is  a  gas,  invis- 
ible as  air  and  but  little  heavier. 

75.  Ozone.  —  Let  strips  of  unsized  paper  be  soaked  in  a 

solution  of  potassium  iodide  mixed  with  starch.     If  these 

strips  be  hung  in  a  jar  of  air,  no  action 

\or  change  will  occur ;  but  if  a  few 
drops  of  ether  be  added,  and  a  hot 
glass  rod  be  put  into  the  jar  (Fig. 
39),  the  paper  will  very  soon  become 
colored  blue.  The  oxygen,  which  at 
first  could  not  attack  the  iodide,  has 
been  changed  by  the  ether  and  the 
heat  so  that  it  can.  This  more  active 
form  of  oxygen  is  called  OZONE. 

That  ozone  is  nothing  but  oxygen, 
may  be  proved.  By  passing  electric 
sparks  through  pure  oxygen,  ozone  is 
formed.  Now,  electricity  is  not  a 
kind  of  matter,  and  hence  can  add 
nothing  to,  nor  can  it  take  any  thing 
from,  the  element  oxygen.  Ozone  is  therefore  but  another 
form  of  oxygen.  Moreover,  if  left  alone  in  the  jar,  ozone 
will  in  time  return  to  the  form  of  oxygen. 

Vigorous  as  is  the  chemical  action  of  ordinary  oxygen,  it 
is  still  more  vigorous  in  the  form  of  ozone.  This  is  the  chief 
difference  in  the  action  of  these  two  forms  of  oxygen. 

Ozone  by  Slow  Combustion  of  Phosphorus.  —  Let  a 
stick  of  phosphorus  be  laid  on  a  plate  with  water  deep 
enough  to  half  immerse  it.  Then  let  a  glass  jar  be  inverted 


Fig.  39. 


CHEMISTRY.  87 

over  it.  ^  White  fumes  arise  from  the  phosphorus,  due  to  its 
combination  with  oxygen,  and,  during  this  slow  combustion 
of  the  phosphorus,  a  portion  of  the  oxygen  of  the  air  is 
changed  to  ozone.  )  Its  presence  may  be  shown  by  the  starch 
paper. 

By  Electricity.  —  A  silent  discharge  of  electricity  through 
air  is  able  to  convert  ^-considerable  portion  of  its  oxygen 
into  ozone.  Indeed,  a  stronger  ozone  mixture  can  be 
obtained  in  this  way  than  in  any  other.  There  is  no  way 
known  in  which  oxygen  can  be  wholly  changed  into  ozone. 

Allotropism.  —  Ozone  is  called  an  allotropic  form  of 
oxygen.  Whenever  the  same  element  exists  in  two  forms, 
they  are  said  to  be  allotropic.  And  the  property  of  an  ele- 
ment in  virtue  of  which  it  can  show  different  properties  under 
different  conditions,  is  called  ALLOTROPISM. 

76.  Density  of  Ozone.  —  Whenever  oxygen  is  changed 
into  ozone,  it  is  reduced  in  volume  ;  and  when  the  ozone  is 
changed  back  to  oxygen  again  the  original  volume  is  restored. 
This  proves  that  ozone  is  denser  than  oxygen.  Experiments 
indicate  that  three  volumes  of  oxygen  form  two  volumes  of 
ozone.  If  so,  ozone  is  one  and  a  half  times  heavier  than 
oxygen,  and  its  density  is  24  (H  =  1). 

Explanation.  —  This  can  be  best  explained  by  supposing 
that  the  molecule  of  ozone  contains  three  atoms,  while  that 
of  oxygen  contains  only  two.  We  should  then  have 

3  O2         =         2  O3. 
Oxygen.  Ozone. 

That  is,  three  molecules  of  oxygen  produce  two  of  ozone. 
Thus  the  molecule  of  oxygen  is O  =  O, 

O 

and  the  molecule  of  ozone  is /  \   . 

0  —  0 

It  is  believed  that  it  is  because  the  molecule  of  ozone 
contains  this  extra  atom  of  oxygen,  that  ozone  is  able  to 
convert  substances  into  oxides  more  vigorously  than  can 


88 


CHEMISTRY 


oxygen  itself.  This  extra  atom  is  easily  given  up  to  unite 
with  other  substances,  with  silver  for  example,  while  the  two 
remaining  atoms  form  a  molecule  of  oxygen. 

77.  Occurrence.  —  Ozone  occurs  in  the  atmosphere.    The 
quantity  varies  from  time  to  time.     It  is  often  more  abun- 
dant after  a  thunder-storm,  being  formed  by  the  action  of 
atmospheric  electricity.     It  is  a  powerful  agent  in  cleansing 
the  atmosphere  from  organic  impurities  :  it  decomposes  them, 
and  converts  their  constituents  into  oxides. 

II. — OXYGEN  AND  HYDROGEN. 

78.  The  Combustion   of  Hydrogen.  —  We   have    seen 
that  hydrogen  is  a  very  combustible  gas.     Now,  the  product 


Fig.  40. 

of  its.  combustion  is  WATER.  This  may  be  demonstrated 
by  an  experiment  represented  in  Fig.  40.  Hydrogen  is  set 
free  in  the  bottle  seen  at  the  left  in  the  picture.  It  passes 


CHEMISTRY.  89 

over  through  the  bent  tube  to  the  bottom  of  a  tall  upright 
jar.  This  jar  contains  some  calcium  chloride,  a  substance 
which  has  a  very  strong  attraction  for  water,  but  none  for 
hydrogen.  The  gas,  passing  out  at  the  top  of  the  jar,  will 
be  thoroughly  dry.  Finally  the  hydrogen  issues  from  the 
other  end  of  the  bent  tube  reaching  from  the  top  of  the 
drying-jar,  and  is  set  on  fire.  A  cold  glass  vessel  is  then 
brought  down  over  the  flame  of  burning  hydrogen. 

What  is  the  result?  Instantly  the  walls  of  the  cold  vessel 
are  dimmed  with  dew  !  The  dew  rapidly  accumulates  ;  and, 
if  the  jar  is  kept  cold,  it  collects  into  little  globules.  The 
little  globules,  grown  larger  and  larger,  at  length  trickle 
down  the  sloping  sides  of  the  vessel,  and  slowly  drop  from 
its  mouth. 

79.  Properties  of  Water.  —  Water  is  a  colorless,  taste- 
less liquid.     It  evaporates  at  all  temperatures,  keeping  the 
atmosphere  charged  with  its  invisible  vapor,   which,   when 
condensed,  produces  fogs  and  mists,  dews  and  rain.     It  boils 
at  100°  C.  (212°  F.).     At  15°  C.  (59°  F.)  water  is  819  times 
heavier  than  an  equal  volume  of  air.     Its  greatest  density  is 
at  a  temperature  of  4°  C.  (39°  F.). 

Freezing.  —  The  freezing  point  of  water  is  0°  C.  (32°  F.) , 
and  on  freezing  it  expands  nearly  ^  of  its  bulk.  Ice  is 
therefore  lighter  than  water  (.917)  when  equal  volumes  are 
compared. 

Ice  is  crystallized  water.  In  solid  masses  the  crystalline 
form  is  obscured,  but  it  is  distinctly  seen  when  the  ice  begins 
to  form.  It  is  beautifully  exhibited  in  the  frost  figures  often 
found  upon  the  window-pane  in  winter,  and  also  in  the  snow- 
flakes  when  just  fallen.  (Fig.  41.) 

80.  Water  as  a  Solvent. — A  great  many  substances  are 
soluble  in  water.     A  substance  is  said  to  be  dissolved  in 
water  when  its  particles  are  so  completely  separated   and 
scattered  through  the  liquid  as  to  be  invisible.     Its  cohesion 
is  entirely  overcome  by  the  stronger  force  of  adhesion  be- 


90 


CHEMISTRY. 


tween  its  particles  and  those  of  water.  A  substance  that 
may  thus  disappear  is  said  to  be  soluble ;  and  the  fluid  which 
contains  it  is  called  a  SOLUTION,  while  that  which  dissolves  it 
is  called  a  SOLVENT.  Salt  is  soluble  in  water :  the  brine  is  a 
solution,  the  water  a  solvent. 


Fig.  41. 

But  it  is  well  known  that  only  a  certain  quantity  of  salt 
can  be  dissolved  in  water  :  all  added  beyond  that,  will  remain 
undissolved.  It  is  so  with  other  solids  :  water  can  only  dis- 
solve a  limited  quantity.  A  solution  in  which  the  fluid  has 
all  it  can  hold  of  a  soluble  body  is  said  to  be  SATURATED. 

Effect  of  Heat.  —  The  solvent  power  of  water  may  be 


CHEMISTRY, 


91 


increased  by  heat.  To  this,  however,  there  are  some  excep- 
tion. Common  salt,  for  example,  will  dissolve  about  equally 
in  hot  and  cold  water,  and  lime  better  in  cold  than  in  hot 
water. 

Solubility  of  Gases.  —  Many  gases,  also,  are  soluble  in 
water.  Oxygen  and  nitrogen  are  examples  :  small  quantities 
of  both  these  gases,  taken  from  the  air,  may  be  found  in  all 
natural  waters.  The  presence  of  this  dissolved  air  in  water 


Fig.  42. 

may  be  proved  easily.  We  only  need  to  place  the  liquid  in 
a  glass  flask,  and  gently  warm  it.  Little  bubbles  of  gas  will 
shortly  be  seen  clinging  to  the  bottom  and  sides  of  the  vessel. 
More  and  more  numerous  and  larger  and  larger  they  become, 
until,  as  the  heat  increases,  they  break  away,  and  escape  at 
the  surface  of  the  water.  These  bubbles  are  bubbles  of  air. 
It  was  in  solution  in  the  water,  and  the  heat  has  driven  it  out. 
It  may  be  caught  in  another  vessel  (Fig.  42)  if  desired. 


92  CHEMISTRY. 

The  experiment  illustrates  the  fact  that  we  may  expel  certain 
gaseous  impurities  from  water  by  boiling. 

Like  solids,  each  gas  has  its  own  degree  of  solubility. 
Oxygen,  for  example,  is  more  soluble  than  nitrogen,  while 
carbon  dioxide  is  much  more  soluble  than  either.  Of  this 
gas,  water  will  dissolve  about  its  own  volume.  Others  are 
still  more  soluble :  of  ammonia  gas,  water  at  0°  C.  will  dis- 
solve 1,148  times  its  volume. 

81.  Natural  Waters.  —  Because  water  can  dissolve  so 
many  other  bodies,  we  may  not  expect  to  find  pure  water 
upon  the  earth.  Coming  from  the  clouds,  it  dissolves  the 
gases  of  the  atmosphere  ;  sinking  into  the  soil,  it  dissolves 
the  minerals  it  meets ;  and  flowing  over  rocks,  it  dis- 
solves their  materials.  Hence  the  waters  of  all  seas,  lakes, 
rivers,  and  wells,  are,  without  exception,  impure  ;  the  kind 
and  quantity  of  their  impurities  depending  on  the  material 
over  which  they  have  passed. 

Mineral  Spring's.  —  Salt  springs  are  those  whose  waters 
have  dissolved  out  the  salt  from  the  soil  through  which  they 
have  flowed.  In  another  place  some  other  substances  may 
exist  in  the  soil  or  rocks  ;  and  the  water,  dissolving  these, 
forms  other  kinds  of  mineral  springs. 

The  water  may,  for  example,  contain  some  salt  of  iron  in 
solution,  in  sufficient  quantity  to  give  it  an  astringent  taste 
and  other  special  properties.  In  this  case  it  is  called 
CHALYBEATE  WATER. 

The  Saltiiess  of  the  Sea.  —  In  a  similar  way  we  may 
account  for  the  saltness  of  the  sea.  Common  salt  is  scat- 
tered in  small  quantities  through  most  soils,  and  is  dissolved 
by  water  which  trickles  through  them.  This  water  collects 
in  rivers,  and  finds  its  way  to  the  sea.  From  the  sea,  water 
can  only  escape  by  evaporation.  But,  by  this  process,  only 
pure  water  passes  away :  the  salt  is  left  behind.  Age  after 
age  this  work  goes  on,  and  large  quantities  of  salt  have  thus 
already  been  accumulated  in  the  sea. 


CHEMISTRY. 


93 


Salt  lakes  are  found,  such  as  the  Great  Salt  Lake  of  Utah. 
They  are  lakes  without  an  outlet ;  so  that,  while  the  water 
may  escape  by  evaporation,  there  is  no  escape  for  the  salt. 

Sucli  Solid  Impurities  increase  the  Weight  of  the 
Water.  —  A  very  pretty  experiment  shows  that  brine  is 
heavier  than  fresh  water.  In 
the  first  place,  a  small  vial  is 
partly  filled  with  a  colored  liquid, 
so  that  when  corked  it  will  just 
sink  in  fresh  water.  Into  a  tall 
jar  (Fig.  43),  put  fresh  water 
several  inches  deep,  and  into 
this  the  little  vial.  Now  by 
means  of  a  long  funnel-tube  a 
saturated  solution  of  salt  may, 
with  care,  be  poured  to  the 
bottom  of  the  jar  without  mixing 
with  the  fresh  water  above. 
The  fresh  water  will  be  lifted, 
floating  on  the  brine,  while  the 


Fig.  43. 
vial,  also  lifted,  marks  the  dividing  line  between  them. 


82.  To  Purify  Water.  —  Water  very  often  contains 
sediment,  —  solid  matter  not  in  solution,  but 
held  suspended  in  the  liquid.  By  long 
standing  this  solid  matter  is  likely  to  fall 
to  the  bottom.  Nevertheless  it  is  often 
desirable  to  separate  it  more  perfectly  or 
more  quickly. 

Filtration.  —  When  a  solid  in  fine  di- 
vision is  mixed  with  a  liquid,  it  may  be 
separated  by  passing  the  liquid  through 
some  porous  substance  which  will  not  let 
the  particles  of  the  solid  pass.  The  pro- 
Fig.  44.  cegg  .g  ca|je(j  jrILTRATION.  The  porous 

body  through  which  the  fluid  passes  is  called  a  FILTER,  and 


94  CHEMISTRY. 

the  clear  liquid  which  issues  is  called  the  FILTRATE.  A  filter 
of  common  form  is  made  of  unsized  paper.  Cut  in  the 
shape  of  a  circle,  it  is  folded  so  as  to  fit  into  a  funnel  (Fig. 
44) .  The  turbid  fluid  poured  upon  it  filters  through ;  and 
the  clear  liquid  is  caught  in  the  vessel  below,  while  the  sedi- 
ment is  left  upon  the  filter. 

On  a  large  scale  water  is  freed  from  its  suspended  matter 
by  passing  it  through  filtering  beds  of  sand  or  gravel. 


Fig.  45. 

Distillation.  —  Impurities  dissolved  in  water  may  be 
either  fixed  or  volatile  matter.  When  the  water  is  boiled, 
only  the  gaseous  impurities  will  pass  away  with  the  steam. 
The  solid  impurities  will  be  left  behind  in  the  boiler,  and  if 
the  steam  be  collected  and  cooled  '>uck  into  water,  the  fluid 


CHEMISTEY.  95 

will  be  free  from  them.  This  process  of  boiling  and  then 
condensing  the  vapor  is  called  DISTILLATION. 

In  Fig.  45,  one  form  of  a  STILL,  as  the  apparatus  for 
distilling  liquids  is  called,  is  represented.  It  consists  of  the 
boiler  and  the  worm.  The  boiler  is  a  close  vessel  standing 
over  a  furnace.  The  worm  is  a  pipe,  usually  of  tin,  bent 
into  a  coil,  and  placed  in  a  vessel  which  is  kept  full  of  cold 
water.  The  boiler  and  worm  are  connected  by  a  steam-pipe. 

The  steam  passing  over  from  the  boiler  enters  the  worm, 
where,  condensed  by  the  low  temperature,  it  becomes  water 
again,  and  may  be  caught  as  it  flows  from  the  bottom. 

To  Remove  Volatile  Impurities.  —  By  boiling  water  in 
an  open  vessel,  such  gases  as  air  and  carbon  dioxide  are 
driven  away.  But  ammonia  and  organic  substances,  which 
may  be  present,  cannot  be  removed  so  easily.  It  is  necessary 
to  put  potassium  permanganate  and  potassium  hydrate  with 
the  distilled  water,  and  then  distill  it  a  second  time.  These 
substances  decompose  the  organic  matter;  and  if -the  first 
portion  of  the  water  which  comes  over  in  this  second  distil- 
lation be  thrown  away,  another  may  be  collected  which  is 
likely  to  be  pure  distilled  ivater. 

By  Freezing1.  —  If  the  quantity  of  solid  impurities  in 
solution  be  small,  water  may  be  purified  from  them  by  freez- 
ing. The  water  only  will  become  ice,  while  the  impurities 
will  be  left  in  the  fluid  which  remains  unfrozen.  On 
re-melting  the  ice  a  purer  water  is  obtained. 

But  where  the  quantity  of  salt  in  the  water  is  large,  there 
is  a  different  result.  The  fluid  must  be  cooled  to  a  much 
lower  degree,  and  then  a  portion  of  the  salt  enters  into  com- 
bination with  the  water  to  form  the  crystals  which  are 
deposited.  In  the  case  of  common  salt  the  crystals  begin 
to  form  at  —  7°  C.,  and  they  are  composed  of  salt  and  water 
in  proportion  represented  by 

NaCl  +  2H2O. 
On  remelting  these  crystals,  salt-water  is  obtained.     Many 


96  CHEMISTRY. 

other  salts,  in  the  same  way,   combine  with  ice  ;   and  these 
new  compounds  have  been  called  CRYOHYDRATES. 

83.  Hard   and   Soft   Water.  —  Water    which    contains 
compounds  of  lime  or  magnesia   in   solution    is   familiarly 
called  HARD  WATER.     The  magnesia  may  be  present  as  a 
sulphate,  and  the  lime  as  a  carbonate,  which  is  soluble  in 
water  containing  carbon  dioxide. 

A  water  is  hard  when  it  requires  much  soap  to  make  a 
lather.  Now,  soap  is  a  salt,  which  contains  a  fatty  acid 
combined  with  a  base  ;  and  these  salts  of  lime  and  magnesia 
decompose  the  soap,  and  combine  with  its  acid  constituent. 
The  new  compound  is  insoluble  in  water,  and  adheres  to  the 
surface  of  whatever  is  being  washed. 

To  Soften  Hard  Water.  —  If  the  water  is  hard,  because 
of  the  presence  of  lime  carbonate,  it  may  be  softened  by 
boiling ;  for,  by  boiling,  the  carbon  dioxide  is  driven  away, 
and  the  carbonate,  no  longer  soluble,  will  settle  as  a  precipi- 
tate. Or,  by  adding  some  "milk  of  lime"  (calcium 
hydrate,  Ca  H2  O2,  and  water) ,  the  free  carbon  dioxide  may 
be  removed,  and  the  water  softened.  If  water  is  hardened 
by  a  sulphate,  it  can  not  be  softened  in  these  ways  :  its  hard- 
ness is  permanent. 

84.  Hydrogen  Dioxide.  —  A  second  compound  of  hydro- 
gen and  oxygen,   and  the  only  one  beside  water,  is  H202, 
called  HYDROGEN  DIOXIDE.     It  is  prepared  by  the  action  of 
dilute  sulphuric  acid  on  pure  barium  dioxide  ;  thus,  — 

BaO2      +      H2SO4      =      BaSO4     +       H2O2. 
Barium      ,      Sulphuric  Barium       ,      Hydrogen 

dioxide  acid  sulphate  dioxide. 

The  dioxide,  H2O2,  remains  dissolved  in  water,  but  by  care- 
fully evaporating  the  water  the  dioxide  may  be  obtained. 

85.  Properties.  —  Hydrogen  dioxide  is  a  colorless,  oily 
liquid,  almost  one  and  a   half  (1.452)    times  heavier   than 
water.     It  has  no  smell,  but  it  has  an  astringent  taste.     If  in 


CHEMISTRY.  97 

contact  with  the  skin,  it  raises  a  white  blister.     It  destroys 
vegetable  colors. 

This  compound  is  very  unstable,  decomposing  sponta- 
neously at  15°  C.,  and  at  100°  C.  so  rapidly  as  sometimes 
to  produce  explosion.  The  products  are  water  and  oxygen. 
The  presence  of  finely  divided  silver  or  gold  decomposes  it 
with  great  violence,  while,  curiously  enough,  the  metal  itself 
remains  unchanged. 

86,  Hydroxyl.  —  Hydroxyl  is  the  name  given  to  half  a 
molecule  of  the  hydrogen  dioxide :  the  formula  for  the  di- 
oxide being  H2  O2,  that  of  hydroxyl  is  H  O. 

This  group  of  atoms,  H  O,  is  found  in  a  large  number  of 
compounds.  Thus  we  find  it  in  sodium  hydrate,  Na  H  O  ;  in 
potassium  hydrate,  KHO;  in  calcium  hydrate,  Ca  (HO)2; 
and  in  alcohol,  C2  H5  H  O. 

It  is  believed  that  in  a  great  many  chemical  changes  this 
group  remains  unbroken.  The  hydrogen  and  the  oxygen 
atoms  cling  together,  and  go  together  into  combination,  and 
stay  together  in  the  new  molecule.  The  group  is  univalent. 
This  is  shown  by  its  constitutional  formula,  H — 0 — . 

III.  —  OXYGEN  AND  CHLORINE. 

87.  Oxides  and  Acids  of  Chlorine.  —  The  chemical  at- 
traction between  chlorine  and  oxygen  is  very  feeble.     Still 
there  are  three  oxides  of  chlorine  known,  —  the  monoxide 
C12  O,  the  trioxide  C12  O3,  and  the  peroxide  Cl  O2. 

The  first  two  of  these  oxides  combine  with  water  to  form 
acids  ;  thus  :  — 

C120  +  H20  =  2HC10, 

Chlorine  monoxide  +  Water  =   Hypochlorous  acid. 

C12O3  +     H2O  =  2HC1O2, 

Chlorine  trioxide  -f-  Water  =       Chlorous  acid. 

In  addition  to  these,  there  are  two  other  acids  of  chlorine : 

Chloric  acid HC1O3, 

Perchloric  acid HC1O4. 


98  CHEMISTRY. 

88.  Chloric  Acid.  —  In  this  series  of  seven  compounds, 
the  chloric  acid  is  the  most  important.  Even  this  one  is  im- 
portant, only  because  it  yields  a  valuable  class  of  salts,  — 
the  chlorates.  Potassium  chlorate  is  an  example. 

Hypochlorous  Acid.  —  Next  in  importance  is  the  hypo- 
chlorous  acid,  which  is  of  interest  chiefly  because  it  is  a 
constituent  in  "  bleaching-powder. "  This  useful  substance 
contains  calcium  hypochlorite,  Ca  (C1O)2,  and  its  bleaching 
power  depends  on  this  substance.  The  addition  of  hydro- 
chloric or  sulphuric  acid  liberates  its  chlorine,  and  this 
chlorine  then  attacks  the  coloring  matter. 

All  these  compounds  of  chlorine  and  oxygen  are  very 
unstable  bodies,  decomposing  easily,  and  some  of  them  spon- 
taneously, often  with  explosive  violence. 


REVIEW. 

I. —SUMMARY   OF  PRINCIPLES. 

89.  Oxygen  may  be  obtained  in  many  ways.  It  is  usually 
obtained  by  heating  potassium  chlorate,  K  Cl  O3. 

It  is  produced  by  heating  mercuric  oxide,  Hg  O.  Also  by 
the  electrolysis  of  water. 

Oxygen  is  colorless,  tasteless,  odorless,  a  little  heavier  than 
air,  and  slightly  soluble  in  water. 

It  enters  into  combination  with  all  the  elements,  with  the 
possible  exception  of  fluorine. 

Substances  which  burn  in  air  burn  with  increased  vigor  in 
oxygen,  and  many  substances  which  will  not  burn  in  air  will 
burn  when  heated  in  this  gas. 

The  combining  weight  of  oxygen  is  16 :  its  molecular 
weight  is  32  :  its  molecular  formula  is  O2  or  O  =  O. 

Oxygen  exists  in  an  allotropic  form,  called  Ozone.  In  this 
condition  it  attacks  and  combines  with  many  things  for 
which,  in  its  ordinary  state,  it  has  no  affinity. 


CHEMISTRY.  99 

The  molecular  formula  for  ozone  is  03,  or  /  \  .     Having 

0  —  0 

three  atoms  in  the  molecule  instead  of  two,  its  density  is  f , 
or  1.5,  that  of  oxygen. 

The  compounds  of  oxygen  are  very  numerous.  Whether 
produced  by  common  oxygen  or  by  ozone,  their  composition 
is  the  same  :  they  are  called  oxides. 

Oxygen  is  the  most  abundant  element  in  nature. 

Oxygen  and  hydrogen  form  two  compounds,  viz.  :  Water 
or  Hydrogen  Oxide,  H2O,  and  Hydrogen  Dioxide,  H2O2. 

Water  is  the  sole  product  of  the  combustion  of  pure  hydro- 
gen. 

Water  consists  of  hydrogen  and  oxygen  in  the  proportion 
of  1  :  8  by  weight.  By  volume  the  proportions  are  two  of 
hydrogen  to  one  of  oxygen. 

The  graphic  formula  for  water  is  H — O — H.  An  atom 
of  oxygen  links  together  two  atoms  of  hydrogen  to  form  a 
molecule. 

The  power  of  water  as  a  solvent  is  very  great.  Heat 
generally  increases  the  solubility  of  solid  bodies  in  water ;  it 
diminishes  the  solubility  of  gases. 

Rain-water,  caught  after  much  has  fallen,  is  the  purest 
form  of  water  to  be  found  in  nature. 

All  spring- water  contains  soluble  salts  and  gases.  If  these 
substances  are  present  in  sufficient  quantity  to  impart  special 
properties  to  the  water,  it  is  called  mineral  water. 

Water  may  be  purified  by  filtration  or  by  distillation :  by 
filtration  it  may  be  freed  from  sediment ;  by  distillation  it  may 
be  freed  from  all  solids  and  most  of  its  gaseous  impurities. 

The  presence  of  salts  of  lime  and  magnesia  renders  water 
unable  to  dissolve  soap  readily ;  such  waters  are  called  hard 
waters. 

Hydrogen  dioxide  is  a  colorless  liquid,  nearly  one  and  a 
half  times  heavier  than  water.  It  readily  decomposes  into 
oxygen  and  water. 


100  CHEMISTRY. 

Its  graphic  formula  is  H — 0 — 0 — H. 

Hydroxyl  is  a  compound  of  one  atom  eaci  of  hydrogen 
and  oxygen.  Its  graphic  formula  is  H — O — .  One  of  the 
bonds  of  the  oxygen  atom  is  free.  In  other  words,  the  mole- 
cule is  univalent. 

This  group,  HO,  is  found  in  a  large  number  of  com- 
pounds. 

Oxygen  and  chlorine  form  three  oxides  of  chlorine.  There 
are  also  four  acids  with  chlorine. 

All  these  compounds  are  very  unstable. 

Chloric  acid  is  important  because  it  forms  a  large  and  use- 
ful class  of  compounds,  the  Chlorates. 

Hypochlorous  acid  is  important  because  some  of  its  salts 
are  bleaching  agents.  The  calcic  hypochlorite  is  the  bleach- 
ing agent  in  u  bleaching  powder,"  often  called  "  chloride  of 
lime." 

II. —EXERCISES. 

Describe  the  preparation  of  oxygen.      Write  the  reaction. 

What  weight  of  oxygen  will  be  furnished  by  one  thousand 
grams  of  potassium  chlorate  ? 

How  much  by  volume,  the  density  of  oxygen  being  16? 

What  weight  of  potassium  chlorate  must  be  used  to 
obtain  ten  liters  of  oxygen  ? 

What  volume  of  oxygen  may  be  obtained  from  one  hun- 
dred grams  of  the  mercuric  oxide,  Hg  O  ? 

What  are  the  physical  properties  of  oxygen  ?  What  is  the 
chemical  action  when  carbon  burns  in  oxygen  ?  When  iron 
burns  in  oxygen?  What  is  the  relation  of  oxygen  to  animal 
life  ?  What  class  of  compounds  does  oxygen  form  ? 

Give  the  atomic  weight  of  oxygen.  Its  atomic  volume. 
Its  molecular  weight.  Its  molecular  volume.  Its  density. 

Where  does  oxygen  occur  in  nature  ? 

How  may  ozone  be  produced  ?  By  what  test  may  it  be 
recognized  ?  In  chemical  character  how  does  it  differ  from 
oxygen? 


CHEMISTRY.  101 

Define  allotropism.  What  evidence  that  ozone  is  au 
allotropic  form  of  oxygen  ?  What  is  the  density  of  ozone  ? 
What  explanation  is  given  ? 

What  is  the  product  when  hydrogen  is  burned  ? 

What  is  the  composition  of  water  by  volume  ?  By  weight  ? 
What  is  its  freezing  point  ?  Its  boiling  point  ?  What  is  the 
temperature  of  water  at  its  greatest  density  ? 

Define  solution.     Solvent.     What  is  a  saturated  solution? 

What  is  the  effect  of  heat  upon  solubility  ? 

What  are  mineral  waters  ? 

Define  filtration.  Evaporation.  Distillation.  Filtrate. 
Distillate.  Describe  the  process  of  distillation. 

What  are  cryohydrates  ? 

What  are  "  hard  waters  "  ?  How  may  hard  water  be  soft- 
ened? 

What  is  the  composition  of  hydrogen  dioxide  ?  How  may 
it  be  obtained?  What  are  its  properties?  What  are  the 
products  of  its  decomposition? 

What  is  hydroxyl  ?  In  what  is  this  group  of  atoms  found  ? 
What  is  its  quantivalence  ? 

Name  the  oxides  of  chlorine.  How  many  acids  of  chlo- 
rine are  known  ?  Which  of  these  are  important  ?  What  is 
bleaching- powder  ? 

IV.  —  SULPHUR. 

90.  Preparation.  —  By  far  the  greater  part  of  sulphur  in 
commerce  has  been  obtained  from  the  "  native  sulphur," 
such  as  is  found  in  Sicily,  simply  by  the  application  of  heat. 
The  sulphur  is  vaporized,  and,  passing  over  into  large  cold 
chambers,  the  vapor  is  again  condensed.  In  this  way  sul- 
phur in  the  finest  powder,  known  in  commerce  as  FLOWERS 
OF  SULPHUR,  is  obtained. 

When  smaller  chambers  are  used,  their  walls  soon  become 
so  heated  by  the  hot  vapors,  that  the  sulphur  is  kept  in  a 
melted  state.  This  liquid,  drawn  off  into  molds  and  cooled, 
forms  what  is  known  as  ROLL  BRIMSTONE. 


102  CHEMISTRY. 

91.  Properties.  —  Sulphur  is  a  solid  at  ordinary  tempera- 
tures.    It  is  tasteless  and  without  odor. 

The  effects  of  heat  on  this  element  are  very  unusuaL  Let 
a  small  quantity  of  sulphur  be  laid  on  a  piece  of  writing- 
paper,  and  held  over  the  flame  of  a  candle ;  in  a  little  time  it 
melts  to  a  clear,  yellow  liquid.  The  melting  occurs  at  about 
115°  C.  Again  :  put  more  of  it  into  a  test-tube,  and  heat  it 
gradually.  After  melting,  it  remains  a  clear,  limpid  liquid 
up  to  about  132°  C.,  and  then  begins  to  get  thick  and  dark- 
colored.  At  about  250°'  C.  it  is  so  viscid  that  it  can  scarcely 
be  poured  from  the  tube ;  but,  as  the  heat  increases,  it 
becomes  less  viscid  again,  and  finally,  at  about  450°  C.  it 
boils. 

If,  when  heated  to  almost  tbe  boiling  point,  the  mobile 
liquid  is  poured  into  cold  water,  it  becomes  curiously  unlike 
common  sulphur ;  it  cools  into  a  dark-colored  solid,  with  a 
considerable  degree  of  elasticity.  In  this  condition  it  is 
called  PLASTIC  SULPHUR.  On  standing,  it  soon  becomes 
yellow  a«f  brittle  again. 

92.  Crystalline  Forms.  —  Sulphur  may  be  obtained   in 
crystals,  either  by  melting  it  or  by  dissolving  it. 

If  we  fill  a  test-tube  one-half  full  of  sulphur,  and  melt  it, 
and  then  let  it  cool  slowly,  we  may  soon  see  the  formation  of 
crystals,  which  grow  from  the  cool  sides  of  the  tube  toward 
the  center  of  the  liquid.  These  crystals  will  multiply  until 
they  crowd  one  another  more  and  more  so  that  the  whole 
finally  becomes  a  compact  mass. 

If  we  desire  to  keep  the  crystals  separate,  we  may  melt  the 
sulphur  in  a  beaker,  let  it  cool  slowly  until  a  good  crop  has 
formed,  then  pierce  the  crust  on  top,  and  pour  off  the  remain- 
ing liquid.  Fine  transparent  needle-shaped  crystals  of  sul- 
phur will  line  the  walls  of  the  beaker. 

These  experiments  illustrate  the  production  of  crystals  by 
the  method  of  fusion.  Crystals  may  also  be  obtained  by  the 
method  of  solution. 


CHEMISTRY.  103 

Crystals  by  Solution.  —  Sulphur  is  not  at  all  soluble  in 
water,  but  it  dissolves  easily  in  carbon  disulphide.  The  car- 
bon disulphide  is  very  volatile :  it  rapidly  evaporates  on 
exposure  to  air,  and  deposits  the  sulphur  in  the  form  of 
crystals.  These  crystals  are  not  needle-shaped  like  those 
obtained  by  fusion  :  they  are  rhombic  octahedrons  instead. 

Sulphur  is  not  the  only  substance  which  is  able  to  crystallize 
in  two  distinct  forms.  Such  substances  are  said  to  be 
DIMORPHOUS. 

93.  Chemical  Properties.  —  Sulphur  has  a  wide  range 
of  attractions.     It  unites  with  oxygen  and  with  hydrogen  to 
form  important  acids.     With  the  metals  it  forms  a  numerous 
class  of  compounds  called  SULPHIDES.     These  were  formerly 
called  sulphur ets. 

94.  Sulphur  in  Nature.  —  In    some    volcanic    districts 
sulphur  is  found  free.     The  mines  of  sulphur  on  the  island 
of  Sicily  contain  the  sulphur  mixed  with  earthy  matter,  and 
much  more  rarely  in  the  form  of  very  pure  and  beautiful 
crystals. 

Sulphur  is  found  in  combination  with  metals  in  the  earth 
almost  everywhere.  Iron  pyrites,  so  common  and  familiar, 
is  a  disulphide  (Fe  S2) .  In  combination  with  hydrogen  it  is 
found  in  the  water  of  what  are  called  sulphur-springs.  And, 
besides  all  this,  sulphur  is  an  important  element  in  many 
animal  and  vegetable  substances. 

95.  Its  Uses.  —  Sulphur  is  very  largely  used  in  the  arts. 
It  is  a  constituent  of  gunpowder  and  of  sulphuric  acid.     It 
is  used  in  the  manufacture  of  friction-matches,  in  medicine 
also  ;  and  in  its  elastic  state,  produced  under  the  influence  of 
heat,  it  is  used  in  taking  casts  of  coins  and  medals. 

V.  —  SULPHUR  AND  HYDROGEN. 

96.  Sulphuretted    Hydrogen.  —  Two    compounds    of 
sulphur  and  hydrogen  are  known.     They  are  represented  by 
the  formulas  H2S  and  H2S2.     The  first^ot^Msae^  hydrogen 


104 


CHEMISTRY. 


sulphide,  or,  as  it  has  long  been  called,  sulphuretted  hydro- 
gen (H2S),  is  an  indispensable  substance  in  the  laboratory, 
and  it  is  that  which  is  dissolved  in  the  waters  of  the  so-called 
sulphur-springs,  giving  to  them  their  odor,  taste,  and  medici- 
nal qualities. 

13 


Fig.  46. 

97.  Preparation.  —  Fragments  of  ferrous  sulphide  (FeS) 
are  placed  in  a  bottle  (Fig.  46),  which  is  provided  with  a 
tightly  fitting  cork  and  two  tubes,  one  a  funnel-tube  reach- 
ing nearly  to  the  bottom,  the  other  a  bent  tube  reaching  from 
the  cork  over  into  the  water  of  a  cistern.     Dilute  sulphuric 
acid  is  poured  through  the  funnel-tube.     Chemical  action  at 
once  begins,  and  the  sulphuretted  hydrogen  is  set  free. 

FeS     +     H2SO4     =   FeSO4    +         H2S, 
Ferrous         Sulphuric  _    Ferrous    _,     Sulphuretted 
sulphide  acid         "   sulphate   "        hydrogen. 

98.  Properties.  —  Hydrogen  sulphide  is  a  colorless  gas, 
having  a  powerful  and  unpleasant  odor,  resembling  the  odor 
of  rotten  eggs.     Very  small  proportions  of  the  gas  mixed 
with  air  render  it  unpleasant ;   while  the   gas   itself,   when 
inhaled,  acts  as  a  powerful  poison.     Very  dilute  chlorine  is 
an  antidote  to  this  poison.     Should  an  antidote  ever  be  re- 
quired, then  moisten  a  towel  witli  dilute  acetic  acid,  sprinkle 
a  few  grains  of  bleaching-powder  upon  it,  fold  the  powder 


CHEMISTRY. 


105 


inside,  and  apply  the  outside  to  the  nose.     The  acid  liberates 
the  chlorine,  and  the  chlorine  attacks  the  hydrogen  sulphide. 
Reaction  with  Metals.  —  Sulphuretted  hydrogen  is  very 
readily   decomposed   by   many   metallic   compounds,    whose 
metals  are  in  this  way  converted  into  sulphides.     Thus,  — 


CuS04  + 
Copper  , 
sulphate 


H2S       =      H2S04 

Hydrogen  __   Sulphuric 
sulphide  acid 


+     CuS, 
,      Copper 
sulphide. 


This  power  to  convert  metals  into  sulphides  renders 
hydrogen  sulphide  an  indispensable  reagent  in  the  laboratory. 

Solubility.  —  This  gas  is  freely  soluble  in  cold  water. 
The  solution  is  easily  prepared  by  passing  the  gas  through 


Fig.  47. 

successive  bottles  of  water,  arranged  as  represented  in 
Fig.  47.  The  sulphide  still  retains  its  odor  and  its  chemical 
power,  and  the  solution  can  be  used  for  chemical  purposes 
instead  of  the  gas. 

VI.  —  SULPHUR  AND  OXYGEN. 

99.  Oxides  and  Acids.  —  Sulphur  and  oxygen  form  two 
oxides :  — 

Sulphurous  oxide S  O2, 

Sulphuric  oxide   .     . S  O3. 


106 


CHEMISTRY. 


By  combining  with  the  elements  of  water,  these  yield  two 
very  important  acids  :  — 

Sulphurous  acid H2  S  O3, 

Sulphuric  acid H2  S  O4. 

Oxides  which  form  acids  by  uniting  with  water  are  often 
called  ANHYDRIDES.  The  S  O2  nmy  be  called  sulphurous 
anhydride,  and  the  S  O3,  sulphuric  anhydride. 

H20    =  H2S03, 

Water  =   Sulphurous  acid. 


Sulphurous  anhydride 


In  addition  to  the  two  acids  just  named,  six  others  are 
known.  One  of  these  is  thiosulphuric  acid  :  it  was  formerly 
known  as  hyposulphurous  acid.  Its  salts,  then  known  as 
hyposulphites,  are  now  called  thiosulphates  instead.  Sodium 
thiosulphate  is  an  example,  and  a  useful  substance. 


Fig.  48. 

«r 

100.  Sulphurous  Oxide.  —  Set  fire  to  a  piece  of  sulphur 
in  a  deflagrating  spoon,  and  thrust  it  into  a  bottle  of  air 
(Fig.  3).  The  sulphur  burns,  combining  with  the  oxygen, 
and  forms  sulphurous  oxide. 

To  obtain  this  gas  in  a  purer  state,  we  may  treat  copper 


CHEMISTRY.  107 

with  sulphuric  acid.  The  operation  may  be  conducted  in  an 
apparatus  shown  in  Fig.  48.  The  copper  and  acid  are 
brought  together  in  a  retort,  and  heated.  The  gas  may  be 
collected  over  mercury.  Three  new  substances  are  produced  : 
viz.,  copper  sulphate,  water,  and  sulphurous  oxide,  thus  :  — 

Cu      +    2H2SO4   =    CuSO4    +  2H2O  +        SO2, 


101.  Properties.  —  Sulphurous  oxide  is  a  colorless  gas, 
with  a  very  stifling  odor.     It  is  very  soluble  in  water,  but 
when  dissolved  it  is  no  longer  sulphurous  oxide  :  it  has  com- 
bined with  water,  and  has  become  sulphurous  acid.     This  is 
easily  demonstrated  by  pouring  a  little  water  into  a  bottle  in 
which  sulphur  has  been  burned,  and  then  adding  a  little  of 
this  liquid  to  a  beaker  of   blue  litmus  solution.     The  red- 
dening of  the  litmus,  which  immediately  occurs,  declares  the 
acid  character  of  the  solution. 

102.  Bleaching.  —  Both  the  gas  and  its  solution  have 
power  to  remove  colors.     If,  for  example,  a  brightly  tinted 
flower  be  held  over  burning  sulphur,  its  color  disappears. 

This  action  is  employed  in  the  arts  for  bleaching  silk, 
woolen,  and  straw  goods.  For  example,  if  a  milliner  wishes 
to  whiten  her  straw,  she  may  hang  it  in  a  small  chamber, 
which  may  be  nothing  more  than  an  inverted  barrel,  and  then 
burn  some  sulphur  under  it.  The  sulphurous  oxide  enters 
the  straw,  and  discharges  its  color. 

On  a  large  scale  the  slightly  moistened  articles  are  hung 
in  large  chambers  in  which  sulphur-fires  are  kindled. 

103.  A  Reducing-  Agent.  —  Sulphurous  oxide  takes  oxy- 
gen out  of  many  other  substances,  and  reduces  them  to  sim- 
pler forms  of  combination.     If,  for  example,  we  fill  a  bottle 
with  the  gas,  by  burning  in  it  some  sulphur,  and  then  thrust 
into  it  a  glass  rod,  or,  better,  a  shaving  of  wood,  moistened 
with  strong  nitric  acid,  dark  red  fumes  will  soon  make  their 


108  CHEMISTRY. 

appearance.     These   red   fumes  show  that  a  compound  of 
nitrogen  and  oxygen,  N  O2,  is  set  free. 

The  chemical  action  may  be  written  as  follows  :  — 

2HN03     +         SO2         =     H2S04     +   2N02, 

Nitric  acid  +  Sulphurous  =   Sulphuric         Nitrogen 
oxide  acid  peroxide. 

A  substance  which  readily  takes  oxygen  out  of  others  is 
called  a  REDUCING  AGENT.  Sulphurous  oxide  is  valuable  to 
the  chemist  as  a  reducing  agent. 

Nitric  acid,  on  the  other  hand,  readily  imparts  oxygen  to 
other  substances.  In  the  above  illustration  it  gives  oxygen 
to  the  S  O2,  and  oxidizes  it  to  S  O3,  which  then  combines  with 
2  H2  O  to  produce  the  H2  S  O4.  A  substance  which  readily 
parts  with  oxygen  to  other  substances,  as  nitric  acid  does,  is 
called  an  OXIDIZING  AGENT.  Nitric  acid  is  valuable  to  the 
chemist  as  an  oxidizing  agent. 

104.  Preparation  of  Sulphuric  Acid.  —  Sulphuric  acid 
is  made  by  oxidizing  sulphurous  oxide  in  presence  of  water. 
The  oxidizing  agent  employed  is  nitric  acid,  or  a  compound 
of  nitrogen  and  oxygen  such  as  the  nitrogen  peroxide,  N  O2. 

On  a  large  scale  the  sulphurous  oxide  is  obtained  by  burn- 
ing sulphur,  or  iron  pyrites  (Fe  S2)  which  yield  sulphur  when 
heated.  This  sulphurous  oxide  is  carried  over  into  immense 
chambers,  which  are  made  of  sheet-lead.  As  it  enters  the 
first  lead  chamber,  it  meets  with  nitric  acid,  which  falls 
through  it  in  fine  streams,  and  also  with  steam,  which  is 
blown  in  from  a  boiler.  The  sulphurous  oxide  is  changed 
into  sulphuric  acid,  which  condenses  on  the  walls  of  the 
chamber,  and  trickles  down  to  the  floor,  where  it  remains 
dissolved  in  water. 

The  nitric  acid  is  thus  reduced  to  nitrogen  monoxide,  N  0  ; 
but  this  unites  at  once  with  the  oxygen  of  the  air  in  the 
chamber,  and  becomes  nitrogen  peroxide,  N  O2. 

This  nitrogen  peroxide  gives  half   its  oxygen  to  change 


CHEMISTRY.  109 

another  portion  of  S  02  to  S  03,  which,  in  presence  of  steam, 
becomes  H2  S  O4,  and  is  itself  again  reduced  to  N  0. 

Again,  the  N  O  becomes  N  02  by  taking  oxygen  from  air  ; 
and,  again,  the  N  O2  oxidizes  another  portion  of  S  02.  In 
this  way  the  N  O  is  a  carriage  which  conveys  oxygen  from 
the  air  to  the  sulphurous  oxide,  continually. 

The  fluid  which  collects  on  the  floors  of  the  lead  chambers 
is  very  dilute  sulphuric  acid,  having  a  specific  gravity  of  1.55. 

Oil  of  Vitriol.  —  The  dilute  acid  is  made  stronger  by 
drawing  it  off  into  leaden  pans,  and  heating  it.  The  water 
passes  off  as  steam,  and  the  acid  remains.  In  this  way  the 
acid  is  concentrated  until  it  contains  only  twenty-two  per 
cent  of  water,  or  has  a  specific  gravity  of  1.71.  In  this 
form  it  is  called  OIL  OF  VITRIOL.  Put  up  in  large  bottles, 
incased  in  wood,  called  carboys,  it  is  sold  in  great  quantities. 

Oil  of  vitriol  always  contains  lead  sulphate  taken  from  the 
lead  pans.  To  avoid  this  impurity  the  concentration  is  often 
made  in  vessels  of  glass  or  of  platinum.  Even  then  the  acid 
may  contain  other  impurities,  especially  arsenic,  which  comes 
from  the  pyrites  employed.  To  obtain  pure  sulphuric  acid, 
the  commercial  acid  is  distilled  in  glass  retorts. 

105.  Properties.  —  Pure  sulphuric  acid  is  a  colorless, 
very  heavy,  and  oily  liquid.  The  usual  brown  color  of  the 
"  oil  of  vitriol  "  is  due  to  a  little  organic  matter  which  it 
contains. 

Its  attraction  for  water  is  one  of  the  most  remarkable 
characters  of  this  acid.  Left  in  an  open  bottle,  it  speedily 
takes  moisture  from  the  atmosphere,  and  increases  in  volume. 

The  combination  of  the  acid  with  liquid  water  is  a  source 
of  heat.  Let  a  little  water  be  put  into  a  beaker,  and  about 
four  times  as  much  strong  acid  added.  The  beaker  will  be 
found  too  hot  to  be  handled  with  convenience  ;  and  if  a  test- 
tube  containing  alcohol,  or  even  a  little  water,  be  placed  in 
the  mixture,  its  contents  will  boil  vigorously. 

Many  organic  bodies  are  decomposed  by  sulphuric  acid. 


110  CHEMISTRY. 

They  are  composed  of  carbon,  hydrogen,  and  oxygen  ;  and 
the  acid  seizes  their  hydrogen  and  oxygen  in  the  proportions 
which  form  water,  leaving  the  carbon  behind.  A  piece  of 
white  pine  wood  is  almost  instantly  blackened  in  this  way 
by  contact  with  the  acid,  and  paper  is  also  charred  as  if  by 
fire.  Let  about  50  centimeters  of  the  strong  acid  be  mixed 
with  the  same  volume  of  a  thick  sirup  of  sugar  in  a  tall  jar : 
the  chemical  action  is  violent,  and  the  sugar  is  converted  into 
a  bulky  mass  of  porous  charcoal. 

106.  Uses.  —  Sulphuric  acid  is  regarded  as  the  most  use- 
ful acid  known.     Its  manufacture  is  one  of   the  important 
branches  of  industry.     Probably  more  than  a  million  tons  is 
made  yearly  in  Great  Britain  and  the  United  States. 

It  is  used  in  the  manufacture  of  almost  all  other  chemicals, 
in  the  preparation  of  fertilizers,  in  the  art  of  bleaching,  in 
dyeing,  and  in  calico-printing. 

107.  The  Sulphates.  —  By  action  on  the  metals, sulphuric 
acid  forms  a  large  class  of  compounds,  called  SULPHATES. 
Both  atoms  of  hydrogen  in  its  molecule  (H2SO4),  or  one 
alone,  may  be  displaced  by  atoms  of  metal,  and  hence  two 
classes  of  sulphates  exist.     Thus  with  sodium  we  may  have 
NasSCV    or  NaHSO4.     The  first  is  the  NORMAL  sodium 
sulphate  ;  the  second  is  the  ACID  sodium  sulphate.     A  nor- 
mal salt  is  one  in  which  all  the  replaceable  hydrogen  of  the 
acid  is  removed.     An  acid  salt  is  one  in  which  only  a  part  of 
the  replaceable  hydrogen  of  the  acid  is  removed. 

The  hydrogen  of  an  acid  which  can  be  replaced  by  metals 
is  called  BASIC  hydrogen.  And  sulphuric  acid  is  said  to  be  a 
DIBASIC  acid,  because  its  molecule  contains  two  atoms  of 
hydrogen,  for  which  metallic  atoms  may  be  substituted. 

Most  of  the  sulphates  are  freely  soluble  in  water.  Lead 
sulphate  and  a  few  others  are  but  little  soluble,  while  barium 
sulphate  is  quite  insoluble. 

108.  Tests.  —  If  a  little  barium   chloride  is   added  to  a 
solution  containing  a  sulphate,  or  sulphuric  acid  itself,  th« 


CHEMISTEY.  Ill 

insoluble  barium  sulphate  will  be  invariably  produced.  It 
will  appear  as  a  white  precipitate,  which  will  not  dissolve 
in  hydrochloric  acid.  The  appearance  of  this  precipitate 
declares  the  presence  of  the  acid,  or  its  compounds,  in  the 
suspected  liquid. 

Free  sulphuric  acid  may  be  detected  by  its  charring  organic 
bodies.  Vinegar  has  been  known  to  contain  this  acid.  To 
detect  the  adulteration,  add  a  little  white  sugar,  and  then 
evaporate  the  vinegar  to  dryness  at  a  gentle  heat.  If  a 
black  residue  remains,  it  indicates  the  presence  of  the  acid. 

VII.  —  SELENIUM  AND  TELLURIUM. 

109.  Selenium.  —  Selenium  is  a  solid  element  found  in 
small   quantities,    usually   in    combination,    as   selenides    of 
metals.     Copper,   lead,   and  silver  selenides  are  examples. 
The  element  exists  in  two  allotropic  forms.     In  one  it  is 
soluble  in  carbon  disulphide  (C  S2) ,  in  the  other  it  is  not. 

The  relations  of  selenium  to  electricity  are  most  curious 
and  important.  When  cooled  suddenly  from  a  melted  state, 
it  is  very  brilliant,  dark-colored,  and  a  non-conductor  of 
electricity.  When  cooled  slowly  from  fusion,  it  has  a  dull 
lead- colored  surface,  is  crystalline,  and  is  a  conductor  of 
electricity.  Its  power  to  conduct  is  increased  by  heat.  So 
exceedingly  sensitive  is  it,  that  even  the  heat  of  a  candle- 
flame,  at  a  distance,  will  dimmish  its  resistance  to  the 
passage  of  the  current.  Even  when  the  radiation  from 
the  candle  passes  through  a  layer  of  water,  it  still  affects  the 
selenium,  indicating  that  the  element  is  affected  not  only  by 
heat  but  by  light  alone,  since  water  transmits  the  light  but 
absorbs  heat. 

110.  Application.  —  The  rapidity  with  which   selenium 
will  respond  to  the  touch  of  light  is  remarkable.     Let  the 
light  be   flashed  on   and  off   in   quick   succession,  and   the 
resistance  of  the  selenium  changes  with  equal  rapidity. 

This  principle  has  been  applied  by  Graham  Bell  in  his 


112  CHEMISTRY. 

photophone.  Light  is  thrown  upon  a  mirror  which  reflects  it 
to  a  distant  selenium  receiver,  lenses  being  employed  to  con- 
centrate it.  This  receiver  is  placed  in  circuit  with  a  battery 
and  a  Bell  telephone.  If  the  voice  is  thrown  against  the 
back  of  the  mirror,  the  mirror  will  vibrate  and  put  the  beam 
of  light  in  motion.  The  motion  of  this  light  on  the  surface 
of  the  selenium  varies  its  resistance.  The  current  of  elec- 
tricity passing  through  it  is  thus  thrown  into  undulation. 
These  undulations  of  the  current  correspond  to  those  of  the 
voice,  and  affect  the  ear  at  the  telephone  in  the  same  way. 
Thus  has  this  property  of  selenium  been  made  useful  in  the 
transmission  of  sound  by  light. 

111.  Tellurium.  —  Tellurium   is   even    more    rare    than 
selenium.     When   pure   this    element    is    bluish-white    and 
lustrous.     In  physical  properties  it  resembles  the  metals,  but 
its  chemical  actions  are  much  like  those  of  selenium  and 
sulphur. 

VIII.  —  THE  BIVALENT  OR  OXYGEN  GROUP. 

112.  Chemical   Resemblance   of   these   Elements. — 

Oxygen,  sulphur,  selenium,  and  tellurium  form  a  well-marked 
natural  group.  They  enter  into  combination  with  the  same 
substances,  and  their  compounds  have  similar  composition. 

This    analogy   is    seen    in    their    hydrogen    compounds. 
Thus :  — 

H20,     H2S,     H2Se,     H2Te. 

Their  bivalent  character  is  clearly  shown  by  these  formulas. 

The  last  three  elements  of  the  group  form  analogous  com- 
pounds with  oxygen.     Notice  the  formulas  :  — 

502,  SeO2,  TeO2, 

503,  Se08,  Te08, 

in  which  this  resemblance  clearly  appears. 


CHEMISTRY.  113 

By  combining  with  water,  these   oxides   all   form   acids. 
Thus :  — 

SeO2  4-     H20    =       H2Se03, 

Selenium  dioxide  +  Water  =  Selenious  acid. 


KEVIEW. 

L  — SUMMARY  OF  PRINCIPLES. 

113.  Sulphur  is  found  in  nature  uncombined. 

This  element  is  a  yellow  solid,  at  ordinary  temperatures 
very  fusible,  easily  vaporized,  but  quite  insoluble  in  water. 

An  allotropic  form  of  sulphur  is  produced  by  heating  it 
to  near  its  boiling-point,  and  suddenly  cooling  it  by  cold 
water.  In  this  condition  it  is  dark-colored  and  elastic. 

The  compounds  of  sulphur  are  very  numerous  and 
important. 

With  hydrogen  it  forms  the  useful  but  unpleasant  "  sul- 
phuretted hydrogen  "  or  hydric  sulphide,  H2S. 

This  gas  is  readily  decomposed  by  many  salts :  their 
metals  take  the  sulphur,  and  become  sulphides. 

With  oxygen  sulphur  forms  two  oxides,  or  anhydrides, 
S  O2  and  S  O8 ;  and  these  unite  with  water  to  form  the 
sulphurous  and  the  sulphuric  acids. 

Both  sulphurous  oxide  and  sulphurous  acid  are  good 
bleaching  agents.  They  are  used  for  bleaching  silk,  woolen, 
and  straw  goods. 

Sulphurous  oxide  is  a  reducing  agent. 

Sulphuric  acid  is  obtained  by  burning  native  sulphur,  or 
iron  sulphide,  and  oxidizing  the  sulphurous  oxide  thus 
formed  by  means  of  nitric  acid  and  the  nitrogen  oxides. 

This  acid  is  the  most  useful  among  chemicals.  It  is  a 
heavy,  oily  liquid,  having  a  strong  attraction  for  water.  It 
combines  directly  with  water,  and  also  decomposes  many 
organic  substances  in  order  to  obtain  their  hydrogen  and 


114  CHEMISTS  Y. 

oxygen,  which  it  takes  from  them  in  the  proportions  which 
form  water. 

This  acid  is  dibasic.  Its  salts  are  sulphates,  and  these  are 
either  normal  sulphates  or  acid  sulphates. 

The  barium  sulphate  is  the  most  insoluble  in  water  or 
acids.  It  is  formed  whenever  a  barium  compound  is  added 
to  a  solution  of  any  sulphate.  It  appears  as  a  white  pre- 
cipitate. This  is  a  test  for  the  presence  of  sulphuric  acid, 
either  when  it  is  free  or  in  combination. 

Selenium  and  tellurium  are  rare  elements,  much  resembling 
sulphur  in  their  chemical  actions. 

Oxygen,  sulphur,  selenium,  and  tellurium  are  bivalent,  and 
constitute  a  well-marked  group,  known  as  the  oxygen  or 
bivalent  group  of  non-metals. 

II.  —  EXERCISES. 

Describe  the  preparation  of  sulphur.  Describe  the  effect 
of  heat  on  sulphur. 

In  what  two  ways  may  crystals  be  obtained  ?  How  may 
we  obtain  crystals  of  sulphur  by  fusion?  How  may  we 
obtain  crystals  of  sulphur  by  solution  ?  Why  is  sulphur  said 
to  be  a  dimorphous  substance?  What  class  of  compounds 
does  sulphur  form?  How  does  sulphur  occur  in  nature? 
What  are  some  of  the  uses  of  this  element? 

What  is  sulphuretted  hydrogen  ?  How  may  it  be  prepared  ? 
Write  the  reaction.  What  are  the  properties  of  this  sub- 
stance ?  What  is  the  chemical  action  of  this  gas  on  metals  ? 
Write  the  reaction  with  Cu  S  O4. 

Name  the  oxides  of  sulphur.  Give  their  composition.  Name 
the  corresponding  acids.  Define  anhydride.  Show  by  the 
equation  that  the  addition  of  the  elements  of  water  converts 
these  oxides  into  acids. 

What  compounds  of  chlorine  are  anhydrides  ? 

How  may  sulphurous  oxide  be  obtained?  Describe  the 
gas.  For  what  purpose  is  it  useful?  . 


CHEMISTRY.  115 

What  is  a  reducing  agent  ?  What  is  an  oxidizing  agent  ? 
Show  by  the  equation  how  S  O2  reduces  nitric  acid. 

How  is  sulphuric  acid  made  ? 

Describe  the  process  as  conducted  on  a  large  scale.  What 
is  oil  of  vitriol  ? 

What  is  the  result  of  bringing  sulphuric  acid  and  water 
together  ?  What  action  does  H2  S  O4  exert  on  organic  bodies  ? 
What  are  some  of  its  uses  ? 

What  class  of  compounds  does  sulphuric  acid  produce? 
What  is  a  normal  salt  ?  What  is  an  acid  salt  ?  What  is  a 
dibasic  acid  ?  A  monobasic  acid  ?  A  tribasic  acid  ?  What 
is  basic  hydrogen? 

What  is  the  test  for  sulphuric  acid?  How  would  you 
detect  this  acid  in  vinegar? 

Name  the  members  of  the  bivalent  group  of  non-metals. 
Give  the  formulas  of  their  hydrogen  compounds.  Give  the 
anhydrides  of  sulphur,  selenium,  and  tellurium. 


SECTION  V. 

THE  TRIVALENT  NON-METALS. 
I.  —  NITROGEN. 

114.  Preparation.  —  There  are  large  quantities  of  nitro- 
gen in  the  atmosphere,  but  there  are  large  quantities  of 
oxygen  with  it.  By  burning  phosphorus  in  a  portion  of  air, 
the  oxygen  will  be  taken  away,  and  the  nitrogen  left.  For 
this  purpose  let  a  piece  of  phosphorus  the  size  of  a  large 
pea  be  placed  on  a  cork  floating  upon  the  water  of  a  cistern. 
Touch  it  with  a  hot  iron,  and  quickly  invert  over  it  a  gallon 
jar.  (See  Fig.  49.)  The  phosphorus  burns  with  a  beautiful 
light,  while  milk-white  vapors  fill  the  jar.  These  vapors  will 
be  gradually  absorbed  by  the  water  which  will  rise  into  the 
jar.  The  space  above  the  water  at  last  is  filled  with  nitrogen. 


116 


CHEMISTRY. 


115.  Its  Physical  Properties.  —  The  nitrogen  is  now 
seen  to  be  a  gas,  perfectly  colorless  and  transparent.  It  is 
without  odor  or  taste,  and  a  little  lighter  than  air,  its  specific 
gravity  (air  =1)  being  .972.  It  is  slightly  soluble  in  water, 
one  hundred  volumes  of  water  absorbing  about  1.5  volumes 
at  ordinary  temperature. 


Pig.  49. 

116.  Its  Chemical  Properties.  —  If  a  lighted  taper  be 
lowered  into  a  jar  of  nitrogen,  it  will  be  extinguished  as 
quickly  as  if  plunged  into  water.  The  gas  will  neither  burn, 
nor  allow  other  things  to  burn  in  it.  So,  too,  if  an  animal 
were  put  into  this  gas,  death  would  soon  follow.  It  is  not 
poisonous,  but  kills  simply  because  it  has  no  power  to  sup- 
port life.  A  bandage  over  the  face,  which  would  shut  all  air 
away  from  the  lungs,  would  kill  in  the  same  way.  These 
facts  illustrate  the  feeble  disposition  of  nitrogen  to  combine 
with  other  elements.  It  can  be  made  to  combine  with  many 


CHEMISTRY.  117 

of  the  elementary  bodies ;  but  the  compounds  are  for  the 
most  part  unstable,  that  is,  easily  decomposed.  On  this 
account  the  compounds  of  nitrogen  are  among  the  most 
energetic  substances  in  chemical  actions. 

The  atomic  weight  of  nitrogen  and  its  density,  hydrogen 
being  1,  are  14. 

117.  Occurrence  in  Nature.  —  Nitrogen  is  a  very  abun- 
dant element.     It  forms  about  four-fifths  by  weight  of  all 
the  atmosphere,  and  besides  this  it  is  an  important  constituent 
in  many  animal  and  vegetable  bodies. 

II. — NITROGEN  AND  HYDROGEN. 

118.  Ammonia.  —  Nitrogen  unites  with  hydrogen  to  form 
a  single  compound :  it  is  the  hydrogen  nitride,  or,  as  it  is 
commonly  called,  ammonia. 

Ammonia  exists  in  small  quantities  in  the  atmosphere,  not 
free  but  in  combination  as  a  carbonate  and  some  other  salts. 
Its  compounds  occur  in  small  quantities  in  rain-water,  and 
are  to  be  found  also  in  all  fertile  soils. 

Nitrogen  is  a  constituent  in  many  of  the  substances  which 
compose  animal  and  some  vegetable  bodies,  and  by  their 
putrefaction  and  decay  ammonia  is  set  free. 

In  this  case  the  nitrogen  and  hydrogen  are  brought  together 
just  at  the  moment  when  they  are  liberated  from  combina- 
tion. At  this  moment  they  unite  in  ammonia.  Substances 
at  the  moment  when  set  free  from  combination  are  said  to  be 
in  the  NASCENT  STATE.  Their  chemical  activity  seems  to 
be  greater  at  this  time  than  at  others :  the  hydrogen  and 
nitrogen,  for  example,  which  readily  unite  in  the  nascent 
state,  show  no  disposition  at  all  to  unite  when  simply  mixed 
together. 

119.  Preparation.  —  Ammonia   is   usually  obtained   by 
heating    together   some    ammonium    chloride   and   ' '  slaked 
lime." 


118  CHEMISTRY. 

The  chemical  change  is  as  follows  :  — 
2NH4C1    +Ca(OH)2=     CaCl2    +  2H2O  +    2NH3, 


That  is  :  two  molecules  of  ammonium  chloride  with  one  of 
calcium  hydrate,  yield  one  molecule  of  calcium  chloride,  two 
of  water,  and  two  of  ammonia. 

120.  Physical  Properties.  —  The    ammonia  obtained  is 
a  gas,  having  a  well-known  pungent  odor.     It  is  much  lighter 
than  air  (.586).     But  its  most  remarkable  physical  property 
is  its  solubility  in  water  ;    one  volume  of   water  at  0°  C. 
absorbing  no  less  than  1,148  volumes  of  the  gas.     As  in  the 
case  of   all  gases,  its   solubility  is  less  at  higher  tempera- 
tures,   but   at  15°   C.  one   volume   of   water  still  dissolves 
783  volumes  of  ammonia.     Its  solubility  may  be  shown  by 
experiment,   using  the  same  apparatus  as  for   hydrochloric 
acid.     The  lower   bottle   should   contain   a   little   reddened 
litmus,  and  the  ammonia  may  be  obtained  by  heating  the 
"  liquor  ammoniae  "  of  the  shops. 

This  '  '  liquor  ammoniae  '  '  is  simply  the  solution  of  the 
ammonia-gas  in  water,  and  it  parts  with  the  gas  at  a  gentle 
heat. 

121.  Chemical  Properties.  —  Ammonia   combines  with 
the    elements    of    water,   and    forms    ammonium  hydrate. 
Thus  :  — 

NH3       +      H20      =  NH4OH, 

Ammonia    +    Water    =    Ammonium  hydrate. 

The  ammonium  hydrate  of  the  laboratory  is  made  by  pass- 
ing ammonia-gas  through  water.  A  few  drops  of  this  solu- 
tion turns  reddened  litmus  blue,  which  shows  it  to  be  a 
hydrate.  Indeed,  it  is  one  of  the  strongest.  But  on  expos- 
ure to  air  the  hydrate  is  decomposed,  and  the  ammonia-gas 
escapes. 


CHEMISTRY.  119 

Ammonia  has  a  strong  attraction  for  hydrochloric  acid. 
Let  two  little  cups  stand  side  by  side  :  into  one  pour  ' '  liquor 
ammonite ";  into  the  other,  hydrochloric  acid.  The  two 
gases  arise,  mix,  combine,  and  a  cloud  of  white  fumes  is 
produced.  The  new  substance  is  ammonium  chloride,  or,  as 
it  was  formerly  called,  sal-ammoniac.  The  presence  of  N  H3 
may  be  tested  in  this  way. 

III.  —  NITROGEN  AND  OXYGEN. 

122.  Nitrogen  Oxides  and  Acids.  —  No  less  than  five 
compounds  of  nitrogen  and  oxygen  are  well  known.     Three 
of  these,  by  uniting  with  the  elements  of  water,  yield  acids. 
The  most  important  of  all  these  eight  compounds  is  nitric 
acid,  H  N  O3. 

123.  Nitric  Acid.  —  This  acid  is  one  of  the  most  impor- 
tant in  chemistry.     It  is  largely  used  in  the  laboratory,  and 
in  great  quantities,  also,  for  many  purposes  in  the  arts.     The 
nitrates  are  a  numerous  class  of  salts,  many  of  which  occur 
in  large  quantities  in  the   earth.     From   these   the   acid  is 
obtained. 

124.  Preparation.  —  Let  potassium  nitrate,  often  called 
saltpeter  and  sometimes  niter,  and  sulphuric  acid  be  heated 
together :  the  nitrate  will  be  changed  to  a  sulphate,  and  the 
nitric  acid  will  be  set  free.     Thus  :  — 

KNO3      +     H2SO4     =        KHSO4        +      HNO3, 
Potassium          Sulphuric         Potassium  acid         xru^n  «ni^ 

».  — r—  •  -«  — —  i     i       .  ~-r~      l.ilLilC'   «iOld* 

nitrate  acid  sulphate 

The  nitrate  is  put  into  the  retort  (Fig.  50) ,  whose  neck  is 
thrust  into  a  receiver  upon  which  a  stream  of  cold  water  runs. 
The  nitric  acid  goes  over  in  vapor  into  the  receiver,  and  is 
there  condensed  into  liquid  form.  This  liquid  has  a  yellow- 
ish color  due  to  the  presence  of  nitric  peroxide. 

Sodium  nitrate  is  much  cheaper  than  niter,  and  is  used 
instead  for  the  manufacture  of  the  acid  for  commerce. 


120 


CHEMISTRY. 


125.  Properties.  —  Nitric  acid  is  a  colorless  liquid  when 
pure,  intensely  acid,  corrosive,  and  poisonous.  Let  it  touch 
the  skin,  and  it  gives  a  yellow  stain  which  time  alone  can 


Pig.  50. 


remove ;  and,  if  long  in  contact,  it  occasions  painful  corro- 
sion. Silk,  wool,  wood,  and  most  organic  bodies  receive  a 
bright  yellow  tint  by  its  action. 

It  is  a  powerful  oxidizing  agent,  as  a  single  experiment 


Pig.  51. 

may  illustrate.  Place  a  little  tin-foil  in  a  cup,  and  pour  dilute 
nitric  acid  upon  it.  Quickly  volumes  of  red  fumes  arise,  and 
the  tin  rapidly  changes  into  a  white  compound  of  tin  and 
oxygen.  The  tin  is  oxidized  by  the  acid. 


CHEMISTRY. 


121 


126.  Nitrons  Oxide.  —  First  in  importance  among  the 
nitrogen  oxides  is  the  lowest  in  the  series,  the  nitrous  oxide. 
It  may  be  obtained  by  heating  ammonium  nitrate.  The 
nitrate  is  put  into  a  flask  (Fig.  51),  from  which  a  bent  tube 
reaches  over  into  a  small  bottle  standing  in  a  vessel  of  cold 
water.  Another  tube  passes  from  this  bottle  over  to  a  jar  on 
the  shelf  of  the  cistern.  By  heat  the  nitrate  is  melted, 
and  afterward  decomposed.  Water  and  nitrous  oxide  are 
formed.  The  water  is  condensed  in  the  cold  bottle,  while 
the  oxide  is  collected  in  the  jar. 

NH4N03          =   2H20  +  N20, 

Ammonium  nitrate  =   Water  -+-  Nitrous  oxide. 

Properties.  —  Nitrous  oxide  is  a  colorless  gas,  a  little 
heavier  than  air.  The  chemical  force  between  its  constitu- 
ents is  weak ;  a  lighted  taper  decomposes  it,  and,  taking  its 
oxygen,  burns  with  almost  as  great  brilliancy  as  in  oxygen 
itself.  When  breathed,  its  effects  upon 
the  system  are  peculiar.  It  often  causes 
a  lively  intoxication,  with  a  disposition 
to  laughter :  for  this  reason  it  has 
been  called  laughing-gas.  It  often 
produces  entire  insensibility,  and  is 
administered  for  this  purpose,  by  sur- 
geons, to  patients  upon  whom  they  are 
to  operate.  If  impure,  or  carelessly 
given,  it  may  produce  serious  results. 

Composition.  — ;  Nitrous  oxide  is 
composed  of  nitrogen  and  oxygen  in  the 
proportions  by  volume  of  two  of  nitro- 
gen to  one  of  oxygen.  This  composi- 
tion is  represented  by  the  formula  N2O. 

The  Experiment.  —  The  apparatus  consists  of  a  eudio- 
meter, shown  in  Fig.  52.  Four  equal  divisions  are  marked 
off  from  the  closed  end  of  the  tube.  Two  of  these  divisions 
are  filled  with  nitrous  oxide  ;  the  remaining  two  are  afterward 


Pig.  52. 


122 


CHEMISTRY. 


filled  with  pure  hydrogen.  By  an  electric  spark  a  violent 
explosion  is  made  ;  steam  is  condensed  on  the  side  of  the 
tube,  and  water  from  the  cistern  will  rise,  leaving  the  two 
upper  divisions  only  filled  with  gas.  This  gas,  when  tested, 
is  found  to  be  nitrogen. 

The  Reasoning-.  —  It  is  clear  that  the  two  volumes  of 
hydrogen  have  taken  oxygen  enough  —  one  volume  — :  from 
the  oxide,  to  form  the  water  that  was  condensed  on  the  tube, 
and  have  left  two  volumes  of  nitrogen.  The  nitrous  oxide, 
then,  was  composed  of  two  volumes  of  nitrogen  and  one  of 
oxygen. 

If  we  represent  equal  volumes  of  the  two  gases  by  equal 
squares,  and  their  names  by  their  symbols,  the  composition 
of  the  compound  may  be  shown  to  the  eye  by  the  following 
diagram :  — 


N 

N 

and  represented  also  by  the  formula  N2  O. 

127.  Nitric  Oxide.  —  Nitric  oxide  may  be  obtained  by 
the  action  of  copper  upon  dilute  nitric  acid,  in  an  apparatus 

similar  to  that  used  in  the 
preparation  of  hydrogen. 
(Fig.  53.) 

The  copper  decom- 
poses the  nitric  acid  ;  red 
fumes  fill  the  bottle  ;  but 
when  the  nitric  oxide 
bubbles  through  the  wa- 
ter into  the  jar  it  is  seen 
to  be  colorless  and  trans- 
parent.  A  lighted  taper 
will  be  instantly  extin- 
guished by  this  gas ;  but  burning  phosphorus  will  decompose  it, 
take  the  oxygen  from  it,  and  burn  with  exceeding  brilliancy. 


CHEMISTEY. 


123 


f  Composition.  —  This  gas  is  decomposed  also  by  heated 
potassium,  and  when  a  measured  quantity  is  used  the  com- 
position of  the  gas  may  be  found.  It  is  composed  of  one 
volume  of  nitrogen  and  one  volume  of  oxygen.  This  compo- 
sition is  represented  to  the  eye  by  the  following  diagram  :  — 


and  its  formula  must  therefore  be  written  N  O. 

128.  Nitrous  Anhydride.  —  Nitrous,  anhydride  is  a  third 
compound  of  nitrogen  and  oxygen,  obtained  with  difficulty 
and  imperfectly  known.  It  has  been  found  to  consist  of  two 
volumes  of  nitrogen  and  three  of  oxygen.  Thus  :  — 


N 

N 

O 

0 

0 

The  f ormula  is  therefore  written  N2  O3. 

_ 

129.  Nitric  Peroxide.  —  If  nitric  oxide  is  :i  allowed  to 
escape  into  the  air,  the  dark  cherry-red  vapors  which  appear 
announce  its  combination  with  oxygen.  This  red  Substance 
is  nitric  peroxide.  By  measuring  the  volumes  of  nitric  oxide 
and  pure  oxygen  needed  to  produce  this  compound,  its  com- 
position has  been  found  to  be,  one  volume  of  nitrogen  to  two 
volumes  of  oxygen.  Hence  the  diagram  :  — 


0 

0 

and  the  formula  which  represents  it  is  N  O2. 
:,The  production  of  this  cherry-red  gas  is  a  useful  test  for 
the  presence  of  free  oxygen.  Whenever  the  presence  of 
oxygen  is  suspected,  we  may  decide  by  passing  into  it  a  little 
nitric  oxide,  which  instantly  unites  with  oxygen  to  yield  the 
red  fumes  of  nitric  peroxide.  -- 


124 


CHEMISTRY. 


130.  Nitric  Anhydride.  —  Finally  we  have  a  compound 
which,  analyzed,  is  found  to  contain  five  volumes  of  oxygen 
and  two  of  nitrogen.  Thus  :  — 


N 

N 

0 

O 

o 

O 

o 

Its  formula  is  N2  O6.     It  is  called  nitric  anhydride  because 
it  unites  with  water  to  form  nitric  acid.     Thus  :  — 

N2O6  +  H2O  =  2HNO3. 

TV.  —  THE  ATMOSPHERE. 
131,  Nitrogen  is  a  Constituent  of  Air.  —  Let  a  jet  of 

hydrogen  be  burned  in  a  bottle  of  air.  For  this  purpose  an 
india-rubber  tube  from  the  bottle  B  (Fig.  54),  ends  in  a  jet- 
pipe,  which  passes  tightly  through  one  of  two  holes  in  a  cork 
which  fits  the  air-bottle  A.  Set  fire  to  the  jet  of  hydrogen, 


Pig.  54. 

and  insert  it  in  the  air-bottle,  whose  neck  may  then  be 
quickly  lowered  into  water.  The  hydrogen  burns  for  a  while, 
and  then  ceases,  the  water  in  the  mean  time  rising  a  little 
distance  into  the  bottle. 

If  the  jet-pipe  be  now  removed,  and  the  remaining  gas 
tested,  it  will  be  found  to  be  nitrogen.  Hence  nitrogen  is  a 
constituent  of  the  air. 


CHEMISTRY.  125 

132.  Oxygen  is  a  Constituent  of  Air.  —  We  have  seen 
that  mercury,  when  heated  for  a  long  time  in  air,  is  changed 
to  a  red  oxide  of  mercury,  and  that  if  this  oxide  is  heated  to 
a  higher  temperature  the  metallic  mercury  will  be  restored 
while  oxygen  will  be  given  off.     Now  observe :  the  oxygen 
set  free  from  the  oxide  in  the  last  heating  must  have  been 
taken  from  the  air  in  the  first.     The  experiment  teaches  that 
oxygen  is  a  constituent  of  air. 

Carbon  Dioxide  is  a  Constituent  of  Air.  —  Let  a 
goblet  of  lime-water  stand  for  a  few  hours  exposed  to  the 
air :  a  crust  will  be  formed  on  its  surface.  This  crust  con- 
sists of  the  well-known  calcium  carbonate.  This  substance 
is  always  formed  when  lime-water  comes  in  contact  with  car- 
bon dioxide,  and  its  presence  in  this  experiment  shows  that 
this  contact  has  occurred,  and  hence  that  air  contains  carbon 
dioxide. 

133.  Water  is  a  Constituent  of  Air.  —  That   a  vessel 
of  ice- water  on  a  warm  day  will  in  a  little  time  be  covered 
with  drops  of  dew,  is  a  fact  sufficiently  familiar.     Now,  the 
water, collected  on  the  vessel,  can  have  come  only  from  the 
air.     It  must  have  been  in  the  air  in  the  form  of  invisible 
vapor,  which,   cooled   by  the   cold  sides  of   the  vessel,   is 
condensed.     Hence  water  is  a  constituent  of  the  air. 

134.  The  Proportions  of  Nitrogen   and   Oxygen.  — 

By  far  the  larger  part  of  the  atmosphere  consists  of  nitrogen 
and  oxygen  :  their  proportions  may  be  found  by  experiment. 
A  vessel,  V  (Fig.  55),  has  two  openings  closed  with  stop- 
cocks, c  and  d.  To  the  upper  stop- cock  is  attached  a  series 
of  tubes,  one,  £,  with  a  bulb  in  which  is  put  some  copper  to 
be  heated  by  a  lamp  below  ;  others,  p  j>,  containing  potash  ; 
and  others  still,  a  a,  containing  sulphuric  acid. 

The  capacity  of  the  vessel  is  accurately  known,  and  at  the 
beginning  of  the  experiment  it  is  quite  full  of  water.  When 
the  stop-cocks  are  opened,  air  will  flow  through  the  series  of 
tubes,  entering  at  o,  until  the  vessel  is  filled.  In  passing 


126 


CHEMISTBY, 


through  a  a,  all  its  water  will  be  taken  out  by  the  acid ;  in 
going  through  p  p,  all  its  carbon  dioxide  will  be  taken  by 
the  potash ;  in  passing  over  the  heated  copper  in  the  bulb 
it  will  give  up  all  its  oxygen ;  and  the  nitrogen  will  be  left 
to  enter  the  globe  alone. 


Fig.  55. 

Now  notice :  if  the  tube  t  be  accurately  weighed  before 
and  after  the  experiment,  what  it  has  gained  will  be  the 
weight  of  the  oxygen  taken  from  the  air  that  passed  through 
it.  The  vessel  V  is  filled  with  the  nitrogen  from  the  same 
air;  and,  since  the  capacity  of  the  vessel  is  known,  the 
weight  of  the  gas  may  be  calculated.  By  this  means  it  has 
been  found  that  one  hundred  parts  of  air  from  which  water 
and'  carbon  dioxide  have  been  taken,  contain,  by  weight, 
76.9  parts  of  nitrogen  to  23.1  parts  of  oxygen. 

135.  The  Proportions  of  Water  and  Carbon  Dioxide. 

— -Now,  the  quantities  of  water  and  carbon  dioxide  might 
also  be  found  in  this  experiment  by  weighing  the  tubes  in 
which  they  are  left,  were  it  not  that  in  so  small  a  quantity  as 
the  vessel  full  of  air  they  are  too  small  to  be  very  appre- 
ciable. If,  however,  larger  quantities  of  air  are  passed,  the 
increase  in  weight  will  be  quite  enough.  It  has  been  found 
that  the  quantities  of  these  substances  vary  at  different  times 
and  places,  being  always  very  small. 

The  quantity  of  water  is  exceedingly  variable.     It  depends 


CHEMISTRY.  127 

upon  locality  and  temperature.  At  15°  C.  the  largest  quan- 
tity that  air  can  hold  is  gx0  of  its  own  weight.  Commonly 
the  amount  is  far  less  than  this. 

The  proportion  of  carbon  dioxide  is  usually  given  by 
volume.  It  varies  from  ^0  to  more  tnan  TWTT>  averaging 
about 


136.  The  Air  is  a  Mixture.  —  In  the  properties  of  the 
atmosphere  we  discover  none  that  do  not  belong  to  one  or 
another  of   its  constituents.     The  oxygen  causes  bodies  to 
burn,    not   so   freely,  of  course,  as   if  it  were   pure.     The 
nitrogen,   if  pure,   would  quench  all  flames  ;    in   the  air  it 
hinders  the  burning  which  it  can  not  quench.     So,  too,  the 
water-vapor,  by  being  cooled,  is  condensed  into  clouds  and 
rain-water,  just  as  this  substance  when  pure   first   becomes 
visible  as   white  vapor  and  then   changes  to   water.     And 
finally,  the  carbon  dioxide  of  the  air  turns  lime-water  white 
just  as  the  pure  gas  would  do,  only  in  a  less  degree.     Hence 
the  air  is  a  mixture  of  its  constituents,  not  a  compound. 

137.  Diffusion.  —  The  gases  of  the  atmosphere  have  very 
different  densities.     The  oxygen  is  heavier  than  the  nitrogen, 
and  the  carbon  dioxide  is  still  heavier  than  oxygen.     Yet  the 
atmosphere  is  a  uniform  mixture  of  these  gases  ;  the  heavy  .and 
the  light  remain  mixed  at  all  heights  above  the  earth.     Left 
to  the  force  of  gravity  they  would  separate  into  layers,  the 
heaviest  at  the  bottom.     Evidently  they  are  under  some  other 
influence  which  overcomes  this  tendency  ;  and  this  mixing  of 
gases  of  different  densities,  when  brought  in  contact,  is  called 
DIFFUSION.     The  same  action  is  also  observed  in  liquids. 

138.  The  Diffusion  of  Liquids.  —  If  in  a  tall  jar  some 
colored  water  is  placed,  alcohol  may,  with  care,  be  poured 
upon  it  without  mixing*  the  fluids.     Being  lighter  than  water, 
the  alcohol  floats  ;  and,  being  colorless,  the  line  of  division 
may  be  distinctly  seen.     After  a  few  hours  the  liquids  in  the 
jar  will  be  found  colored  uniformly  throughout.     The  heavy 


128  CHEMISTRY. 

water  has  risen ;  the  lighter  alcohol  has  sunk,  and  a  uniform 
mixture  is  formed.  Liquids,  which  when  shaken  together, 
will  remain  mixed,  will  diffuse  when  brought  in  contact ;  but 
those  which  separate  again  when  standing  a  while  will  not 
diffuse. 

Osino.se  of  Liquids.  —  A  thin  membrane  or  porous  sub- 
stance will  not  prevent  liquids  from  mixing.  To  illustrate  : 
let  a  bladder  be  firmly  tied  over  the  end 
of  a  lamp-chimney,  or  other  glass  tube  ; 
and,  being  filled  with  alcohol,  let  it  be 
pressed  a  little  way  into  a  vessel  of 
water  (Fig.  56).  After  a  time  the 
fluid  will  be  seen  gradually  rising  in 
the  chimney.  The  water  flows  in  to 
mix  with  the  alcohol,  and  a  smaller 
quantity  of  alcohol  flows  out  at  the 
same  time.  This  mixing  of  liquids 
through  porous  solids  is  called  OSMOSE. 

139.  The  Diffusion  of  Gases.  — 

Diffusion  among  gases  is  more  rapid 
than    among   liquids.      The   following 

experiment  will  clearly  illustrate  this  important  property. 
Two  strong  bottles  with  narrow  necks,  one  filled  with  oxygen, 
the  other  with  hydrogen,  are  placed  with  their  open  necks 
together,  the  oxygen  being  at  the  bottom.  After  considerable 
time  the  gases  in  both  bottles  will  explode  at  the  touch  of  a 
lighted  taper.  Neither  oxygen  nor  hydrogen  is  explosive, 
but  their  mixture  is.  The  oxygen  must  have  risen  into  the 
upper  jar,  and  the  hydrogen  must  have  fallen  into  the  lower 
one,  until  a  mixture  was  formed  in  both.  Gases  diffuse  in 
spite  of  gravitation  ;  nor  will  other  mechanical  forces  pre- 
vent them  :  a  gas  will  spread  in  direct  opposition  to  a  current 
of  air. 

On  examination  it  is  found  that  hydrogen  will  diffuse  four 
times  as  fast  as  oxygen.     Now,  the  densities  of  these  gases 


CHEMISTRY.  129 

are  as  1  :  16;  but  notice,  their  diffusive  rates  are  as  4  :  1 .  In 
other  words,  their  diffusive  rates  are  inversely  as  the  square 
roots  of  their  densities.  This  law  applies  to  the  diffusion  of 
all  gases. 

The  Osmose  of  Gases.  —  Porous  substances  can  not 
stop  the  mixing  of  gases.  Hydrogen  can  not  for  any  length 
of  time  be  kept  pure  in  india-rubber  bags :  it  will  pass 
through  the  pores  to  mix  with  the  air  outside. 
The  osmose  of  hydrogen  and  air  may  be 
shown  very  beautifully  with  the  apparatus 
seen  in  Fig.  57.  A  porous  cup  (of  Grove's 
battery)  is  fitted  air-tight  to  a  tube  which 
reaches  into  colored  liquid,  contained  in  a 
bottle.  If  a  jar  of  hydrogen  is  held  over  the 
cup,  bubbles  instantly  rush  out  of  the  tube, 
showing  that  hydrogen  has  entered  to  mix 
with  the  air  inside.  Nor  is  this  all :  if  the 
jar  is  removed,  the  liquid  quickly  rises  in  the 
tube,  showing  that  the  hydrogen  leaves  the 
cup,  to  mix  with  the  air  outside,  and  that  it 
flows  out  so  much  faster  than  air  can  flow  in, 
that  a  partial  vacuum  is  formed. 

Application  to  the  Air.  —  We  can  now 
see  how  gases  of  such  different  weights  as 
those  which  form  the  atmosphere  are  kept 
uniformly  distributed,  instead  of  forming 
layers  with  the  heaviest  at  the  bottom.  In 
obedience  to  this  law  of  diffusion,  the  heavier 
gases  are  compelled  to  rise,  and  the  lighter  ones  to  fall,  until 
the  proportions  of  them  all  are  the  same  throughout.  Think, 
moreover,  how  vast  the  quantities  of  unwholesome,  and  even 
poisonous  gases,  which  are  given  off  by  decaying  substances, 
and  from  sewers,  swamps  and  marshes.  Were  gases  subject 
only  to  the  laws  of  gravitation,  the  heavy  and  poisonous  car- 
bon dioxide,  with  miasms  and  effluvia,  would  render  animal 
life  impossible. 


130  CHEMISTRY. 


V.  —  PHOSPHORUS. 

140.  Phosphorus  in  Nature.  —  Compounds    containing 
phosphorus  are  quite  common  in  soils  and  rocks.     Plants  re- 
ceive them  from  the  soil ;  while  animals,  living  upon  vegetable 
food,  take  these  compounds  from  the  plant.     They  are  found 
in  wheat  and  other  grains,  and  in  the  brain  and  secretions  of 
animals  ;  so  that,  while  not  a  very  abundant  element,  phospho- 
rus is  widely  distributed  and  very  important.     Its  most  com- 
mon compounds  are  the  phosphates,  and  of  these  the  most  com- 
mon is  the  calcium  phosphate.     This  compound  of  phosphorus 
occurs  in  bones,  and  from  these  the  element  is  obtained. 

141.  Its  Physical  Properties.  —  Phosphorus   is  a  solid 
element,  having  a  pale  yellow  color,  rather  soft  and  wax-like 

at  common  temperature,  but  brittle  at 
0°  C.  In  a  dark  room  its  clean  sur- 
face shines  with  a  feeble,  pearl-white 
light.  Its  vapor  also  is  beautifully 
phosphorescent.  To  show  this,  put  a 
few  small  fragments  of  the  solid  into 
a  flask  of  water,  and  boil  it.  The 
mixed  vapors  of  water  and  phospho- 
rus escape  (Fig.  58),  and,  in  a  dark 
room,  look  like  livid  flames  issuing 
from  the  mouth  of  the  flask,  while  at 
the  same  time  globules  of  melted 
phosphorus,  on  the  surfaces  of  the 
water  and  the  glass,  appear  like  little 
Fig.  58.  balls  of  pearl. 

This  element  is  insoluble  in  water  ;  but  it  dissolves  freely  in 
ether,  and  still  more  freely  in  carbon  disulphide. 

142.  Its  Chemical  Properties.  —  Phosphorus  combines 
most   readily  with   oxygen.      From   a   piece   of    the   solid 
exposed  to  air,  white  fumes  are   continually  falling,  which 
consist  of  a  compound  of  phosphorus  and  oxygen.     A.  gentle 


CHEMISTRY.  131 

heat  —  that  of  the  fingers  handling  it  is  often  enough  — 
causes  it  to  burst  into  violent  combustion,  forming  the  fumes 
in  great  abundance.  On  this  account  the  element  must  be 
kept  under  water ;  and  it  should  tye  held  under  water  when 
cut,  lest  the  friction  of  the  knife  set  it  on  fire.  The  pieces 
to  be  used  should  be  afterward  dried  by  gentle  pressure 
between  layers  of  blotting-paper. 

There  is,  however,  an  allotropic  form  of  phosphorus, 
called  red  phosphorus,  which  will  not  produce  the  phenom- 
ena of  combustion  under  a  temperature  of  260°  C.  Ex- 
periments with  this  variety  are,  of  course,  far  less  dangerous 
than  with  the  common  form.  Sticks  of  the  solid,  exposed 
to  light,  gradually  change  to  red  phosphorus. 

This  element  is  a  violent  poison  :  even  its  vapors,  inhaled, 
will  cause  wasting  disease. 

143.  Uses.  —  The  most  important  use  of  phosphorus  is 
in  the  manufacture  of  matches,  hundreds  of  tons  being 
employed  annually  for  this  purpose. 

Formerly  the  match  was  made  by  first  dipping  the  end  of 
the  wood  into  melted  sulphur  and  afterward  into  a  paste  of 
gum- water,  phosphorus,  and  either  niter  or  potassium  chlorate. 
By  friction  the  phosphorus  is  set  on  fire.  The  heat  of  the 
burning  phosphorus  is  intense  enough  to  ignite  the  sulphur, 
which  in  turn  inflames  the  wood.  But  sulphur  is  seldom  now 
employed,  its  place  having  been  taken  by  paraffine  or  stearic 
acid.  When  potassium  chlorate  is  used,  the  match  burns 
with  an  explosive  combustion. 

The  "  safety  match,"  now  in  quite  common  use,  contains 
no  phosphorus.  This  element  is  put  upon  the  box,  the  sur- 
face on  which  the  match  is  rubbed,  instead  of  upon  the 
match  itself.  The  matter  on  the  tip  of  this  match  contains 
potassium  chlorate  and  sulphur  or  antimony  sulphide,  and 
sometimes  red  lead  and  potassium  bichromate.  The  matter 
on  the  side  of  the  box  contains  red  phosphor  as.  Only  by 
rubbing  the  match  against  this  surface,  can  it  be  easily  fired. 


132  CHEMISTRY. 


VI. — PHOSPHORUS  AND  HYDROGEN. 

144.  Hydrogen  Phosphide.  —  Three  compounds  of 
phosphorus  and  hydrogen  are  known.  One,  PH3,  is  a  gas 
at  ordinary  temperatures  ;  another,  P2  H4,  is  a  liquid  ;  and  a 
third,  P2  H,  is  a  solid. 

The  gaseous  compound  may  be  obtained  by  the  action  of 
phosphorus  on  a  solution  of  '"  caustic  potash,"  KHO.  The 
experiment  is  represented  in  Fig.  59. 


Fig.  59. 

The  small  flask  is  two-thirds  filled  with  a  moderately  strong 
solution  of  potassium  hydrate,  and  a  small  piece  of  phos- 
phorus is  added.  A  few  drops  of  ether  are  poured  in,  and 
the  flask  is  then  closed.  The  delivery  tube  dips  into  a  cistern 
of  water. 

On  applying  a  gentle  heat  the  ether  evaporates,  and  its 
vapor  expels  the  air  from  the  flask  and  tube.  Very  soon 
bubbles  of  gas  arise  from  the  phosphorus  ;  and  after  a  time 
larger  bubbles  emerge  from  the  tube  in  the  water,  come  in 
contact  with  the  air,  and  instantly  take  fire  with  explosion. 
The  bright  white  flame  is  followed  by  a  beautiful  vortex-ring 
of  white  vapor  (P2O5)  rising  and  expanding,  and  finally 
breaking  and  vanishing  in  the  air. 


CHEMISTRY.  133 

And  yet  the  gaseous  phosphide  is  not  spontaneously 
inflammable,  as  it  would  appear  to  be :  it  has  been  found 
that,  made  in  this  way,  it  contains  some  vapor  of  the  liquid 
phosphide,  and  to  this  the  spontaneous  combustion  is  due. 

VII. — PHOSPHORUS  AND  OXYGEN. 

145.  Phosphoric    Oxide    and    Acid.  —  When     phos- 
phorus burns  in  dry  oxygen,  or  in  a  full  supply  of  dry  air,  a 
snow-white  solid  is  produced  :  it  is  the  phosphorus  pentoxide, 
P2O5,    also   called   phosphoric   anhydride.      This   snow-like 
solid  has  so  strong  an  attraction  for  water,  that  exposed  to 
the  air  it  takes  moisture  and  melts  away,  or  if  brought  in 
contact  with  water  itself  the  two  unite  with  such  vigor  as  to 
produce  a  hissing  sound,  and  much  heat.     The  powder  can 
be  preserved  only  in  hermetically  sealed  flasks. 

If  now  some  drops  of  the  solution  of  this  oxide  are  added 
to  blue  litmus,  the  color  instantly  changes  to  red,  showing 
the  liquid  to  be  an  acid.  The  P2  O5  has  combined  with  3  H2  O, 
yielding  2  H3  P  O4,  or  two  molecules  of  phosphoric  acid. 

146.  Phosphorous  Oxide  and  Acid.  —  If,    instead    of 
burning  the  phosphorus  rapidly,  it  be   made  to  burn   slowly 
in  a  small  supply  of  dry  air,  it  produces  a  different  com- 
pound.    The  phosphorous  trioxide,  P2O3,  is  formed. 

This  phosphorous  oxide  is  also  a  white  solid,  and  when 
brought  into  contact  with  water  instantly  unites  with  it. 
The  P2  O3  takes  3  H2  O,  and  yields  2  H  3  P  O3,  or  two  molecules 
of  phosphorous  acid. 

147.  Other   Acids.  —  Besides   the   two   acids   of   phos- 
phorus just  mentioned,  there  are  three  others,  whose  names 
and  composition  are  here  given  for  reference :  — 

Hypophosphorous  acid H3PO2, 

Metaphosphoric  acid H  P  O3, 

Pyrophosphoric  acid H4  P2  O7. 


134  CHEMISTEY. 

VEIL  —  ARSENIC. 

148.  Arsenic  in  Nature.  —  Arsenic  sometimes  occurs  in 
the  earth  uncombined  with  other  substances  ;  but  generally 
it  is  found  as  an  oxide  or  a  sulphide,  mixed  with  similar 
compounds  of  the  metals.     "  It  was  at  one  time  supposed 
that  arsenic  entered  into  the  composition  of  the  flesh  and 
bones  of  animals  as  a  normal  constituent ;  but  it  has  been 
clearly  proved  that  it  is  never  found  in  the  tissues,  either  of 
animals  or  vegetables,  except  when  it  has  been  introduced 
into  them  by  accident  or  design."     (BRANDE  &  TAYLOR.) 

Its  Physical  Properties.  —  Arsenic  is  a  very  brittle 
solid,  in  appearance  much  like  metals.  It  may  be  sublimed 
by  heat ;  that  is  to  say,  it  may  be  changed  from  the  solid  to. 
the  vapor  state,  directly,  without  melting. 

Its  Chemical  Properties.  —  Heated  in  the  open  air, 
arsenic  rapidly  combines  with  oxygen,  and  even  on  simple 
exposure  to  air  it  forms  an  oxide.  With  some  of  the  metals 
it  forms  arsenides.  Owing  to  the  criminal  use  of  its  poison- 
ous compounds,  this  element  has  been  most  thoroughly  and 
successfully  studied. 

IX.  —  ARSENIC  AND  HYDROGEN. 

149.  Hydrogen  Arsenide.  —  Let  fragments  of  zinc  be 
put  into  a  bottle  (Fig.  60)  with  water  enough  to  cover  them. 
Let  sulphuric  acid  be  poured  through  the  funnel-tube  until 
a  brisk  evolution  of  hydrogen  begins.     Patiently  wait  until  all 
air  has  been  driven  out  of  the  bottle,  and  then  touch  a  match- 
flame  to  the  tip  of  the  taller  tube  from  which  the  gas  is 
escaping.     The  almost  colorless  flame  of  hydrogen  is  thus 
obtained. 

Next  pour  in  through  the  funnel  a  few  cubic  centimeters 
of  a  solution  of  arsenious  oxide  As2  O3 :  a  moment  afterward 
the  flame  will  become  enlarged,  and  shine  with  a  livid  white- 
5ss. 
The  hydrogen  has   decomposed  the  arsenious  oxide,  and 


.7.XVIILSITY) 

CHEMISTRY.  135 

taken  its  arsenic  to  form  hydric  arsenide,  As  H8,  commonly 
called  arseniuretted  hydrogen. 

'Properties.  —  This  substance  is  a  colorless  gas  of 
unpleasant  odor,  and  very  poisonous. 
It  is  very  combustible,  and  the  prod- 
ucts of  combustion  are  water  and 
arsenious  oxide.  If  the  flame  be 
cooled  by  holding  the  cold  surface  of 
a  piece  of  porcelain  across  it,  then 
only  the  hydrogen  will  burn  away ; 
the  arsenic  will  be  deposited  on  the 
porcelain  in  the  form  of  a  brown  and 
lustrous  mirror.  ' 

150.  Marsh's  Test.  —  This  repro- 
duction of  arsenic  as  a  mirror  on 
porcelain  is  a  most  delicate  and  im- 
portant test  for  the  presence  of  the 
compounds  of  this  poisonous  sub- 
stance.  It  is  known  as  Marsh's  test. 
It  is  applied  by  means  of  the  apparatus  shown  in  Fig.  61, 


Fig.  61. 

Into  the  bottle  A  are  put  pure  zinc,  water,  and  sulphuric  acid 
for  the  evolution  of  hydrogen  gas.     This  gas  is  allowed  to 


136  CHEMISTRY. 

flow  until  all  air  is  expelled  from  the  apparatus.  The  liquid 
supposed  to  contain  the  poison  may  be  afterward  poured 
through  the  funnel-tube.  The  gas  formed  in  the  bottle, 
passing  through  the  bulb,  6,  loses  a  part  of  the  water  carried 
over  with  it,  and  going  over  calcic  chloride  in  c,  it  is 
thoroughly  dried.  It  finally  escapes  at  the  pointed  end  of 
the  tube,  d.  After  the  air  of  the  apparatus  has  been  all 
driven  out  by  the  stream  of  gas,  the  hydrogen  may  be  burned 
as  it  issues. 

Now,  if  the  liquid  contain  arsenic,  there  is  at  once  formed 
arseniuretted  hydrogen  (H3As).  In  presence  of  much 
arsenic  the  color  of  the  flame  turns  to  a  livid  hue,  and 
sometimes  gives  off  white  fumes  of  arsenious  oxide.  But 
now  comes  the  decisive  test.  A  cold,  clean,  white  porcelain 
surface  is  held  in  the  small  flame  for  a  moment ;  metallic 
arsenic  condenses  on  its  surface,  if  the  poison  is  present, 
and,  when  cold,  appears  a  blackish-brown  stain,  with  a  bright 
metallic  luster.  The  substance  of  this  stain  may  be  still 
further  tested,  until  the  last  doubt  of  its  character  is 
removed. 

The  experiment  is  varied  by  applying  heat  to  the  middle 
part,  o,  of  the  small  tube.  The  arseniuretted  hydrogen,  if 
present,  will  be  decomposed,  and  the  metallic  arsenic  will 
lodge  upon  the  inside  surface  of  the  tube,  forming  a  brilliant, 
mirror-like  ring. 

By  Marsh's  test,  even  so  little  as  0.01  of  a  milligram 
(ToVtf  gr-)  can  be  detected  with  certainty. 

This  is  only  one  of  many  tests  by  which,  taken  together, 
the  chemist  can  pronounce  upon  the  presence  of  arsenic  with 
absolute  certainty. 

151.  Some    other    Compounds    of    Arsenic.  —  The 

arsenious  oxide  (As2O3)  is  the  common  "arsenious  acid" 
or  "  white  arsenic,"  — the  well-known  poison.  It  is  a  white 
solid,  slightly  soluble  in  water,  with  which  it  forms  an  acid, 
and  this  acid  combines  with  metals  to  form  arsenites. 


CHEMISTRY.  137 

These,  also,  are  violent  poisons ;  and  yet  some  of  them  are 
used  quite  largely  in  the  manufacture  of  aniline  dyes,  in 
calico-printing,  and  as  pigments.  Green  wall-papers,  many 
of  them,  have  been  colored  with  copper  arsenite,  well  known 
as  Scheele's  green.  Nor  is  green  the  only  color  of  wall- 
papers containing  arsenic :  it  has  been  found  in  yellow,  pink, 
blue,  and  drab.  These  arsenical  papers  are  guilty  of 
poisonous  action  upon  those  who  inhabit  the  rooms. 

Another  compound  of  arsenic  and  oxygen  has  the  formula, 
As2  O5 :  it  is  the  arsenic  oxide.  This  oxide  is  also  an  anhy- 
dride, since  it  unites  with  water  to  form  arsenic  acid.  This 
acid  is  represented  by  the  formula,  H3  As  O4. 

As2O6  -|-  3  H2O  =  2  H3AsO4. 

By  passing  sulphuretted  hydrogen  through  a  solution  of 
arsenious  oxide,  made  acid  by  a  few  drops  of  hydrochloric 
acid,  a  fine  yellow  precipitate  is  formed  at  once.  This  yellow 
solid  is  arsenious  sulphide,  As2  S8.  It  has  long  been  known 
under  the  name  of  orpiment,  and  was  formerly  much  used 
as  a  pigment  called  king's  yellow. 

X.  —  BORON. 

152.  Boron  in  Nature.  —  The    element    boron    is    not 
found  free  in  nature,  but  several  of  its  compounds  exist  in 
considerable   quantities.     The  most  important  of  these  are 
boric  or  boracic  acid,  and  sodium  biborate,  commonly  called 
borax. 

The  Element.  —  Boron  is  sometimes  a  dark-brown  pow- 
der, and  sometimes  it  occurs  as  lustrous  crystals  almost  as 
hard  as  diamond.  In  neither  of  these  allotropic  forms  does 
boron  show  much  chemical  activity.  Boron  is  the  only  non- 
metal  which  forms  no  compound  with  hydrogen. 

153.  Boracic  Acid.  —  The    waters    of    the    lagoons    of 
Tuscany  hold  this  acid  in  solution.     These  waters,  evaporated 
by  the  heat  of  volcanic  jets  of  steam  issuing  in  the  neigh- 


138  CHEMISTRY. 

borhood,  yield  the  acid  in  solid  form.  This  is  the  source  of 
it  for  the  European  market. 

In  the  United  States  it  is  manufactured  from  the  native 
borax  found  in  sufficient  quantity  in  the  water  of  the  borax 
lake  in  California. 

Let  a  little  borax  be  dissolved  in  two  and  a  half  times  its 
weight  of  boiling  water,  and  add  a  little  more  than  half  its 
weight  of  strong  hydrochloric  acid.  On  cooling,  this  solution 
will  deposit  glistening  plate-like  crystals.  These  crystals  are 
boracic  acid. 

Place  a  little  of  this  crystallized  acid  in  a  capsule,  and  add 
a  spoonful  of  alcohol.  After  stirring  it  well,  to  dissolve  the 
acid,  set  fire  to  the  solution,  stirring  it  the  while,  and  the 
flame  will  exhibit  a  fine  green  color.  This  is  a  characteristic 
test  for  this  acid. 

154.  The    Berates.  —  With    sodium    this     acid    forms 
sodium   biborate,    or   borax,   Na2B4O7.     With  other  metals 
other  borates  are  produced,  the  class  being  quite  numerous. 

Many  of  these  are  crystalline,  and  in  the  form  of  crystals 
almost  always  contain  water.  Borax,  for  example,  in  crys- 
tallizing, takes  up  ten  parts  of  water,  so  that  its  formula 
becomes  Naj,B4O7+ 10  H2O.  This  water  contained  in  crys- 
tals is  called  WATER  OF  CRYSTALLIZATION.  Oftentimes,  when 
gently  heated,  the  crystals  will  dissolve  in  this  water  which 
they  contain.  Heat  crystals  of  borax  in  an  iron  spoon,  and 
they  "  melt  in  their  water  of  crystallization." 

XI.  —  THE  TRIVALENT  GROUP. 

155.  The  Group.  —  Nitrogen,   phosphorus,   arsenic    and 
boron  are  trivalent  elements.     Many  other  chemical  relations 
also  mark  them,  with  the  exception  of  boron,  as  members  of 
a  natural  group. 

They  are  Trivalent.  —  The  compounds  of  these  elements 
with  hydrogen  have  the  following  symbols  :  — 

H3N,  H3P,  H8As, 


CHEMISTRY.  139 

from  which  we  learn  that  an  atom  of  each  can  hold  three 
atoms  of  hydrogen  in  combination.  These  three  compounds' 
are  gases. 

Other  Chemical  Relations.  —  The  complete  analogy  in 
the  composition  of  the  compounds  of  these  elements  may  be 
seen  by  a  glance  at  the  following  formulas  :  — 

N203,        N204,      N205,        NC13(?), 

P203,        .  .  .        P205,        PC13,          P2S3,        P2S5, 

As2O3,      .  .  .        As2O5,      AsCl3,      •  As2S3,      As2S5. 


REVIEW. 
L— SUMMARY   OP  PRINCIPLES. 

156.  Nitrogen,  phosphorus,  arsenic,  and  boron  are  the 
members  of  the  trivalent  group  of  non-metals,  one  atom  of 
each  being  equivalent  to  three  atoms  of  hydrogen. 

Nitrogen  does  not  directly  combine  with  oxygen.  Phos- 
phorus and  arsenic  do. 

Nitrogen  is  a  colorless  gas ;  phosphorus,  a  translucent 
solid  ;  arsenic  also,  a  splid,  steel-gray  and  metallic. 

Nitrogen  and  hydrogen  form  a  single  compound,  ammonia, 
a  gas,  very  soluble  in  water  with  which  it  combines  to  form 
liquor  ammonite,  a  strong  base. 

Ammonia  combines  directly  with  hydrochloric  acid  to  form 
ammonium  chloride. 

Nitrogen  unites  with  oxygen  to  form  five  compounds, 
illustrating  well  the  "  law  of  multiple  proportions." 

Two  of  these  oxides  are  anhydrides  ;  with  water  one  forms 
nitrous  acid,  and  the  other  nitric  acid. 

Nitric  acid  is  a  powerful  oxidizing  agent. 

Nitrous  oxide  is  an  anaesthetic  much  used  by  dentists. 

Nitric  oxide  is  a  test  for  the  presence  of  oxygen,  with 
which  it  instantly  forms  red  vapors  of  nitric  peroxide. 

The  atmosphere  is  a  mixture  of  nitrogen,  oxygen,  carbon 


140  CHEMISTRY. 

dioxide,  and  water-vapor,  together  with  small  and  variable 
quantities  of  ammonia,  and  several  other  gases. 

Compared  with  the  nitrogen  and  the  oxygen,  the  quantity 
of  all  other  constituents  is  small. 

By  volume,  the  air  consists  of  :  — 

Oxygen 20.77 

Nitrogen 79.23 

100.00 
By  weight,  the  ah*  consists  of  :  — 

Oxygen 22.92 

Nitrogen 77.08 

100.00 

For  most  purposes  it  is  sufficient  to  say  that  four-fifths  of 
the  air  is  nitrogen,  and  one-fifth  is  oxygen. 

Diffusion  is  the  tendency  of  fluids  or  of  gases  to  mix  when 
brought  in  contact.  The  principle  of  diffusion  is  well  illus- 
trated by  the  uniform  mixture  of  gases  throughout  the 
atmosphere. 

Phosphorus  burned  in  a  full  supply  of  air  or  oxygen  yields 
phosphoric  pentoxide,  P2  O5 ;  but  burned  in  a  limited  supply 
it  yields  phosphorous  trioxide,  P2O3. 

These  oxides  are  anhydrides :  one  of  them  with  water 
forms  phosphgric  acid,  the  other  phosphorous  acid. 

These  acids  form  large  classes  of  salts,  one  the  phosphites, 
the  other  the  phosphates. 

The  compounds  of  arsenic  are  remarkable  for  their  poison- 
ous character.  Nevertheless  some  of  them  are  used  in  many 
industrial  arts. 

There  are  two  oxides  of  arsenic  ;  viz.,  the  arsenious  oxide, 
As2  O3,  and  the  arsenic  oxide,  As2  O5. 

These  oxides  are  anhydrides :  with  water,  one  yields 
arsenious  acid,  the  other  arsenic  acid. 

With  metals  these  acids  form  salts :  the  first  yields 
arsenites,  and  the  second  arsenates.  "  Scheele's  green  "  is 


CHEMISTRY.  141 

a  copper  arsenite,  and  Schweinfurt's  green  consists  of  copper 
arsenite  and  acetate.  Both  are  used  as  pigments  in  coloring 
wall-paper. 

The  arsenic  in  paper  can  be  easily  detected.  Moisten  the 
paper  with  hydrochloric  acid,  and  then  add  water.  Into 
this  solution  thrust  a  bright  copper  wire.  Arsenic,  if 
present,  will  be  deposited  on  the  wire,  giving  it  a  gray 
coating. 

The  most  sensitive  and  reliable  test  for  arsenical  poison  is 
Marsh's  test. 

The  antidote  to  arsenical  poison  is  moist  ferric  hydrate, 
which  can  be  made  by  adding  ammonia-water  to  a  solution 
of  iron  sulphate  (copperas),  after  having  first  heated  the 
solution  with  a  little  nitric  acid.  In  absence  of  this  antidote 
milk,  or  white  of  eggs,  may  be  used.  Or  a  powerful  emetic 
may  be  administered. 

Boron  has  two  allotropic  forms,  one  amorphous,  the  other 
crystalline. 

It  is  the  only  non-metal  which  has  no  known  compound 
with  hydrogen. 

Its  most  important  compounds  are  boric  acid  and  borax. 

II. —EXERCISES. 

Give  the  preparation  of  nitrogen.  What  are  its  physical 
properties  ?  What  is  its  chemical  character  ? 

What  are  its  atomic  weight  and  density  ? 

How  does  it  occur  in  nature  ? 

What  compound  does  nitrogen  form  with  hydrogen  ?  What 
is  the  source  of  the  ammonia  in  the  air?  Define  nascent 
state.  What  influence  has  the  nascent  state  on  combination? 

How  is  ammonia  usually  obtained  ?  Give  the  reaction. 
Consult  the  table  of  elements,  and  convert  this  reaction  into 
a  numerical  equation.  What  does  this  numerical  equation 
show?  How  much  ammonium  chloride  is  required  to  yield 
one  hundred  grams  of  ammonia?  To  yield  one  hundred 
liters  of  ammonia? 


142  CHEMISTRY. 

What  are  the  physical  properties  of  ammonia?  What 
is  ammonium  hydrate?  How  is  this  hydrate  made  in  the 
laboratory  ? 

How  many  oxides  of  nitrogen  are  known?  How  many 
oxygen  acids? 

How  is  nitric  acid  prepared?     Give  the  reaction. 

What  are  the  properties  of  nitric  acid?  Why  is  it  called 
an  oxidizing  agent? 

Describe  the  preparation  of  nitrous  oxide.  What  are  its 
properties  ?  For  what  is  it  useful  ?  How  is  its  composition 
represented?  Describe  the  experiment  to  determine  its 
composition.  Give  the  reasoning. 

How  may  nitric  oxide  be  obtained  ?  What  is  the  composi- 
tion of  nitric  oxide  ?  What  formula  represents  its  molecule  ? 
How  does  it  serve  to  test  the  presence  of  oxygen  ? 

Give  the  formula  for  nitrous  anhydride.  The  formula  for 
nitric  peroxide.  The  formula  for  nitric  anhydride. 

What  acid  comes  from  nitric  anhydride?  Show  by  an 
equation  the  composition  of  the  acid  derived  from  nitrous 
anhydride. 

Name  the  two  most  abundant  constituents  of  the  atmos- 
phere. Name  other  constituents.  Give  the  composition  of 
the  air  by  volume.  By  weight.  How  are  these  proportions 
determined? 

What  are  the  proportions  of  water-vapor  and  carbon 
dioxide  ?  Why  is  the  air  called  a  mixture  ? 

Is  this  mixture  uniform  at  all  heights?  On  what  principle 
are  the  ases  kept  from  settling  into  layers?  Define 
diffusion.  State  the  law  of  diffusion  of  gases. 

How  does  phosphorus  occur  in  nature?  What  are  its 
physical  properties?  With  what  element  has  oxygen  the 
strongest  inclination  to  combine?  Describe  the  allotropic 
form  of  phosphorus.  Describe  the  composition  of  the 
match.  What  is  the  safety-match  ? 

How  does  arsenic  occur  in  nature  ?  What  are  its  physical 
properties  ?  Its  chemical  properties  ? 


CHEMISTRY.  143 

How  may  arseniurettecl  hydrogen  be  prepared  ?  What  is 
its  formula?  Describe  its  combustion. 

What  is  Marsh's  test?  Describe  the  apparatus  employed. 
How  is  the  experiment  conducted? 

What  is  the  so-called  "  arsenious  acid  "  ?  What  is  its  true 
chemical  name  ? 

What  is  the  most  remarkable  general  character  of  the 
arsenic  compounds? 

To  what  uses  are  many  arsenical  compounds  applied? 
How  can  the  arsenic  in  wall-paper  be  detected  ? 

Name  the  members  of  the  trivalent  group  of  non-metals. 
Show  that  they  are  trivaleiit  by  means  of  the  formulas  for 
their  hydrogen  compounds.  In  what  else  are  they  analogous  ? 


SECTION   VI. 

THE  QUADRIVALENT  NON-METALS. 
I.  —  SILICON. 

157.  The  Element.  —  Silicon  is  a  solid  substance,  some- 
times obtained  as  a  brown  powder,  sometimes  as  crystals 
with  an  iron-gray  color  and  metallic  luster.     It  is  very  hard, 
very  insoluble,  and  very  difficult  to  melt ;  but  when  heated  in 
air  it  burns  because  of  its  attraction  for  oxygen. 

158.  Its  Compounds.  — -  Silicon  is  never  found  free  in 
nature,  but  its  compounds  are  very  abundant.     With  oxygen 
it  forms  a  silicon  oxide,  Si  O2,  more  commonly  called  silica. 

This  compound  is  one  of  the  most  abundant  substances  in 
the  earth.  The  beautiful  opal  and  amethyst  and  some  other 
gems  are  almost  pure  silica :  so  is  the  more  common  rock 
crystal  or  quartz,  while  the  sand  of  the  sea-shore  and  every 
variety  of  sandstone  rock  are  the  impure  forms  of  the  same 
substance. 

Silica  is  also  an  important  constituent  in  organic  bodies. 
It  gives  strength  to  the  stalks  of  grains  and  grasses,  while  it 


144  CHEMISTKY. 

constitutes  the  skeleton  of  whole  tribes  of  some  of  the  lower 
orders  of  animals. 

Silica  is  used  largely  in  the  manufacture  of  glass. 

Silicic  acid,  H2  Si  O3,  is  a  limpid  liquid  of  little  known 
importance ;  but  its  salts,  the  silicates,  occur  in  large 
quantities  and  are  widely  distributed  in  the  earth. 

159.  Glass.  —  Glass  is  made  from  silica  and  the  bases, 
potash,  soda,  lime,  and  some  others,  according  to  the  variety 
required.  These  materials,  being  intensely  heated,  melt  into 
a  transparent  pasty  mass,  portions  of  which  may  be  taken 
from  the  furnace,  and  blown  or  molded  into  the  different 
forms  in  which  glass  articles  are  made.  These  articles, 
being  afterward  annealed,  are  ready  for  the  market.  We 
may  study  the  manufacture  of  glass  a  little  more  in  detail. 

The  Materials.  —  In  all  true  glasses  silica  is  one  con- 
stituent. This  substance  exists  in  almost  pure  form  in  flint, 
agate,  and  quartz  ;  while  all  varieties  of  sand  consist  of  the 
same  in  various  degrees  of  purity.  Flint  was  formerly  used 
in  the  manufacture  of  glass :  hence  the  name,  flint  glass, 
which  one  variety  still  retains.  Sand  is  now  the  more 
general  source  of  silica,  great  care  being  used  to  select  a 
pure  material. 

Potash,  soda,  and  lime  are  the  most  important  bases  used 
with  the  silica ;  but,  besides  these,  lead  oxide  and  oxides  of 
tin  and  manganese  are  often  employed. 

The  Varieties  of  Glass.  —  There  are  several  varieties  of 
glass,  chief  among  which  are  four,  viz.  :  green  bottle-glass, 
Bohemian  glass,  window-glass,  and  flint-glass. 

Green  bottle-glass  is  made  of  cheaper  and  coarser  material 
than  any  other  variety.  Its  bases  are  more  numerous  :  they 
are  chiefly  soda  and  lime  ;  but  the  oxides  of  iron  and  manga- 
nese are  among  them,  and  to  the  first  of  these  the  glass 
owes  its  familiar  color. 

Bohemian  glass  is  made  from  purer  material  than  bottle- 
glass,  and  care  is  taken  to  have  it  free  from  color.  Its  bases 


CHEMISTRY.  145 

are  potash,  lime,  and  manganese.  Its  lightness,  the  absence 
of  color,  and  its  power  to  stand  high  heat  and  sudden 
changes  of  temperature,  make  it  very  valuable  for  chemical 
purposes. 

Window-glass  consists  chiefly  of  silica,  soda,  and  lime. 

Flint-glass  consists  chiefly  of  silica,  potassa,  and  lead 
oxide  (Pb2  O3) .  This  very  beautiful  variety  of  glass,  some- 
times called  crystal  glass,  is  chiefly  made  into  such  articles 
of  domestic  and  ornamental  use  as  tumblers,  decanters, 
wine-glasses,  and  vases.  It  is  very  transparent,  and  refracts 
light  powerfully :  on  this  account  it  is  valuable  for  lenses, 
and  other  optical  instruments. 

The  Melting-.  —  The  raw  material  is  heated  in  pots  made 
of  the  purest  and  most  infusible  clay,  and  set  in  a  conical 
furnace.  When  the  heat  is  sufficient,  the  silica  and  the 
bases  form  silicates.  In  the  case  of  window-glass,  for  ex- 
ample, the  silica,  soda,  and  lime  form  SODIUM  and  CALCIUM 
SILICATES.  The  compound  of  these  silicates  is  a  transparent 
half-fluid  or  pasty  mass  of  glass,  ready  to  be  wrought  into 
any  desired  form. 

The  Blowing".  —  By  means  of  an  iron  tube  four  or  five 
feet  long,  the  workman  takes  out  of  the  furnace  a  portion  of 
the  pasty  and  adhesive  glass.  He  gives  it  regular  shape  by 
rolling  it  upon  a  smooth  hard  surface,  and  makes  it  hollow  by 
blowing  air  through  the  tube.  By  keeping  the  tube  in  con- 
stant rotary  motion  while  he  blows,  the  bulb  is  enlarged  into 
a  globe  ;  or  if,  at  the  same  time,  he  swings  his  tube,  pendu- 
lum like,  a  pear-shaped  flask  is  made. 

Some  idea  of  the  interesting  process  of  making  window- 
glass  may  be  gained  by  studying  the  following  cuts  found  in 
Muspratt's  Applied  Chemistry.  In  Fig.  62  some  of  the  first 
stages  of  the  process  are  shown.  In  front  of  each  opening 
of  the  furnace  is  a  stage,  built  over  a  pit  about  ten  feet 
deep.  Upon  these  stages  the  workmen  stand.  The  ball  of 
glass  having  been  taken  from  the  furnace,  the  workman  blows 
through  his  pipe,  while  he  at  the  same  time  skillfully  rotates 


146 


CHEMISTRY. 


it  in  his  hand,  and  swings  it  backward  and  forward,  some- 
times below  his  feet,  sometimes  over  his  head,  until  he  has 
lengthened  and  enlarged  it  into  a  cylinder  with  uniform  sides 
as  long  as  the  pane  of  glass  is  expected  to  be.  The  ends  of 
this  cylinder  are  then  cut  off,  and  a  slit  is  made  along  one 
side.  It  is  afterward  placed  upon  a  smooth  and  even  stone 
plate,  and  heated  in  an  oven.  As  the  glass  softens,  the 


Fig.  62. 

workman,  with  an  iron  rod,  presses  the  sides  of  the  cylinder 
open  (see  Fig.  63),  and  finally  smooths  it  out  upon  the  flat 
surface  of  the  stone.  It  is  then  a  pane  of  glass,  needing 
only  to  be  carefully  cooled. 

.  The  Annealing.  —  Annealing  is  a  process  of  slow  cool- 
ing. All  articles  of  glass  must  be  annealed.  For  this  pur- 
pose they  are  placed  in  hot  ovens,  whose  temperature  grows 
gradually  less,  until,  at  the  end  of  four  or  five  days,  they 


CHEMISTRY. 


147 


Fig.  63. 


are  quite  cold.  The  process  is  necessary,  because  if  glass  is 
cooled  suddenly  it  becomes  exceedingly  brittle,  and  will  some- 
times break  even  without  apparent  cause  ;  but  when  slowly 
cooled  it  is  able  to  stand  much  pressure  and  sudden  blows. 

' '  Considered  only  with  reference  to  its  application  in  the 
study  of  natural  phenomena,  it  is  impossible  to  doubt  the 
singular  influence  glass  has  exerted 
on  the  progress  of  science.  It  is 
chiefly  by  its  aid  that  astronomy 
has  attained  a  perfection  so  won- 
derful ;  by  it,  also,  naturalists  have 
been  enabled  to  study  under  the 
microscope  a  host  of  phenomena 
.which  before  escaped  notice.  But 
perhaps  of  still  greater  importance 
is  the  use  made  of  it  by  chemists 
in  their  experiments.  It  requires  no  profound  chemical 
knowledge  to  recognize  the  fact  that  to  glass  is  chiefly  owing 
the  present  advanced  state  of  the  sciences,  so  fruitful  in 
marvelous  application." 

II.  — CARBON. 

160.  Charcoal  obtained  from  Wood.  —  When  splin- 
ters of  wood  are  heated  in  a  test-tube  closed  with  a  cork 
through  which  passes  a  small  tube,  considerable  quantities  of 
vapor  and  gas  escape,  and  the  wood  turns  black.  The  black 
mass  that  remains  when  the  gas  is  no  longer  given  off  is 
charcoal,  one  form  of  carbon.  In  the  same  way,  on  a  large 
scale,  wood  is  put  into  retorts,  and  heated  intensely ;  its 
.liquid  and  gaseous  constituents  are  driven  off,  while  the  solid 
carbon  remains. 

Or,  again  :  if  we  light  one  end  of  a  splinter  of  wood,  and 
slowly  push  the  burning  part  into  the  mouth  of  a  test-tube, 
the  part  in  the  tube  will  only  glimmer  in  the  small  supply  of 
air,  or  be  extinguished  altogether.  The  black  residue  is 
carbon. 


148 


CHEMISTRY. 


On  a  Large  Scale.  —  In  a  similar  way,  when  charcoal  is 
required  m  large  quantities,  piles  of  wood  are  burned  under 
a  covering  of  sod  and  moist  earth,  where  but  little  air  can 

reach  them.  Figs. 
64  and  65  represent 
the  way  in  which  the 
method  is  carried 
out.  In  the  former 
we  see  how  the  sticks 
are  piled  ;  in  the  lat- 
ter we  see  the  pile  in 

Fig.  64. 

its  slow  combustion. 

Air  can  enter  only  through  holes  in  the  earthy  covering  near 
the  base.     Smoldering   sometimes  for   weeks,    the   gaseous 


Fig.  65. 

parts  of  the  wood  are  at  last  all  driven  off  ;  while  the  carbon, 
keeping   the    form   of  the   original   sticks,  with   knots   and 


CHEMISTRY. 


149 


annular  rings  still  perfect,  all,   however,   much  reduced  in 
size  and  weight,  remains. 

Charcoal  is  without  crystalline  form,  and  on  this  account  it 
is  said  to  be  AMORPHOUS. 


161.  Other  Forms  of  Amorphous  Carbon.  —  Beside 
charcoal  there  are  several  other  forms  of  amorphous  carbon, 
among  which  we  may  mention  lamp-black,  coke,  and  animal 
charcoal. 

Animal  charcoal  is  carbon  obtained  from  animal  sub- 
stances. Bone-black,  for  example,  is  animal  charcoal  ob- 
tained by  charring  bones  in  iron  cylinders. 

Coke  is  the  carbon  which  remains  when  soft  coal  is  heated 
to  redness  in  the  ab- 
sence of  air.  Large 
quantities  of  soft,  or 
bituminous  coal,  are 
used  for  the  manufac- 
ture of  illuminating 
gas,  and  large  quan- 
tities of  coke  are  left 
behind.  It  is  a  fuel 
of  considerable  value. 

Lamp  -  Black.  — 
Bodies  which  contain 
large  proportions  of 
carbon  are  likely  to 
burn  with  a  smoky 
flame.  They  are  sure 
to  do  so  if  the  supply 
of  air  in  which  they 
burn  is  limited.  The 
blackness  of  the  smoke 
is  due  to  minute  par- 
ticles of  carbon.  Let  a  metallic  plate  be  held  over  the  flame 
of  an  oil-lamp,  and  we  shall  find  an  abundance  of  this  finely 


Fig.  66. 


150 


CHEMISTRY. 


divided  carbon  deposited  on  it.  In  this  form  the  carbon  is 
called  LAMP-BLACK. 

This  form  of  carbon  is  much  used  in  the  arts.  On 
a  large  scale  it  is  made  by  burning  tar,  resin,  or  petro- 
leum, in  such  a  way  that  but  little  air  will  reach  it.  The 
dense  black  smoke  is  drawn  over  into  large  chambers 
(Fig.  66),  on  whose  walls  the  soot,  or  lamp-black,  is 
deposited. 

Lamp-black  is  used  as  a  black  paint,  and  when  mixed  with 
oil  it  constitutes  printer's  ink.  The  finest  kind  is  also  used 
for  preparing  India  ink  and  in  calico-printing. 

162.  The  Diamond. —  The  diamond  is  crystallized  car- 
bon. A  roughly  rounded 
pebble  found  in  the  sand 
and  clay  of  India  or 
Brazil,  the  diamond  would 
hardly  be  picked  up  by 
one  whose  eye  had  not 
been  trained  to  recognize 
it;  but  when  polished  it  is 
at  once  the  most  beautiful 
and  the  most  indestructible 
of  gems.  It  can  neither 
be  melted  nor  dissolved  :  it 
may,  however,  be  burned 
when  heated  intensely  in 
oxygen-gas. 

Its  great  power  to  re- 
fract light  and  its  wonder- 
ful hardness  are  character- 
istic properties :  these  are 

Fig  67  the  properties  which  render 

the  gem  so  valuable  in  the 

arts.  The  light  flashing  from  the  different  sides  of  the  crys- 
tal makes  it  the  most  brilliant  of  ornaments :  its  extreme 


CHEMISTRY. 


151 


hardness  renders  it  valuable  in  the  construction  of  pivots  in 
delicate  instruments  where  friction  is  to  be  avoided. 

There  are  two  principal  forms  of  this  most  elegant  jewel. 
They  are  called  the  brilliant  and  the  rose.  The  first  of  these 
is  regarded  as  the  finest.  Its  shape  is  well  shown  in  Fig.  67. 
Look  at  the  gem  side  wise,  and  it  appears  as  seen  in  the  upper 
part  of  the  picture  ;  look  at  the  top  of  it,  and  it  appears  as 
seen  in  the  lower  part.  The  form  of  the  rose  is  seen  in 
Fig.  68  ;  a  side  view  above  and  a  top  view  below. 

Value  of  the  Diamond.  — The  diamond  is  the  most 
highly  prized  of  precious 
stones.  Its  value  depends 
on  its  weight,  and  its  freedom 
from  color  and  from  flaws. 
The  weight  of  a  diamond  is 
described  as  so  many  carats, 
a  carat  being  .2054  grm. 
(3.17  grains). 

One  of  the  finest  diamonds 
in  the  world  is  known  as  the 
Pitt  or  Regent  diamond, 
which  weighs  136.25  carats, 
and  is  worth  £125,000,  equal 
to  about  $625,000.  The  lar- 
gest diamond  in  Europe 
weighs  194J  carats:  it  be-  Pig.  68. 

longs  to  Russia,  and  is  set  in  one  end  of  the  emperor's 
scepter.  The  famous  Koh-i-noor  is  the  property  of  the  Engr 
lish  crown.  Originally  it  weighed  186  carats,  but  its 
weight  has  been  reduced  to  106  carats  by  the  recutting  to 
which  it  has  been  subjected. 

163.  Graphite.  —  Graphite  is  another  crystalline  form  of 
carbon.  It  is  also  called  plumbago,  and  is  still  more  famil- 
iarly known  as  black-lead.  It  is  taken  from  the  earth  in 
large  quantities  for  the  manufacture  of  lead-pencils.  It 


152  CHEMISTRY. 

has  a  shining  steel-gray  color,  and  it  is  a  good  con- 
ductor of  electricity,  being  in  these  respects  much  like 
metals. 

164.  Allot ropic  Forms.  —  Charcoal,   the   diamond,  and 
graphite,   are  but  different   forms   of   the   element   carbon. 
They  differ  in  hardness,  in  color,   in  weight,   and  in  many 
other  physical  properties.     They  are  alike  infusible,   alike 
able  to  resist  the  action  of  substances  which  attack  most 
other  bodies,  alike  in  being  combustible,  and  alike  in  yield- 
ing the  same  substance  (carbon  dioxide)  when  burned.    That 
they  are  also  alike  in  being  of  vegetable  origin,  is  believed  ; 
but  of  the  mode  in  which  the  diamond  and  graphite  have  been 
made  from  vegetable  matter,  little,  if  any  thing,  is  known. 

It  is  Found  in  Nature.  —  All  the  different  varieties  of 
coal  are  but  different  impure  forms  of  carbon,  the  remains 
of  a  vegetation  which  grew  ages  before  the  period  of  man's 
creation. 

Enormous  beds  of  limestone  are  found  on  every  continent, 
but  not  a  molecule  of  limestone  occurs  which  does  not  contain 
an  atom  of  carbon. 

And  more  :  not  a  single  organized  body,  from  the  lowest 
form  of  plant  to  the  highest  form  of  animal,  exists,  in  which 
carbon  is  not  an  important  element. 

III.  —  CARBON  AND  OXYGEN. 

165.  Oxides  of  Carbon.  —  With   oxygen   carbon  unites 
in  two  proportions.     We  have 

Carbon  monoxide CO, 

Carbon  dioxide C  O2. 

166.  Carbon   Monoxide.  —  Carbon   monoxide    may   be 
prepared  by  heating  gently,  in  a  flask,  four  or  five  grams  of 
potassium  ferro-cyanide  with  about  ten  times  as  much  strong 
sulphuric   acid.     It  is   a   gas,   and  may  be  collected 
water. 


CHEMISTRY. 


163 


Properties.  —  Carbon  monoxide  is  colorless,  but  has  a 
slight  odor  of  a  peculiar  kind.  It  is  very  inflammable,  and 
burns  with  a  blue  flame,  which  may  be  seen  playing  over  the 
surface  of  a  brisk  and  new-made  coal  fire. 

This  gas  is  very  poisonous.  Even  when  breathed  in  small 
quantities  it  produces  headache  and  giddiness  :  if  the  quan- 
tity is  increased,  insensibility  and  death  follow.  Accidents, 
not  a  few,  have  arisen  from  burning  charcoal  in  open  fires  in 
rooms.  The  carbon  takes  oxygen  from  air  to  form  this 
poisonous  oxide,  which  escaping  into  the  room  destroys 
life. 


Fig.  69. 

167.  Carbon  Dioxide.  —  Carbon  dioxide  may  be  obtained 
from  marble  by  the  following  process.  Small  fragments  of 
marble  are  put  into  a  bottle  whose  cork  is  provided  with  two 
tubes,  one  reaching  to  the  cistern,  the  other  a  funnel-tube 
reaching  nearly  to  the  bottom  of  the  bottle.  (Fig.  69.) 
Water  is  poured  through  the  funnel  until  the  lower  end  of 
its  tube  is  covered,  and  hydrochloric  acid  is  then  added. 
A  violent  agitation  quickly  begins  in  the  bottle :  carbon 
dioxide  is  set  free,  and  is  collected  in  the  jar  over  the 
water. 


154 


CHEMISTRY. 


Marble  is  the  calcium  carbonate  represented  by  Ca  C  O3. 
The  reaction  with  hydrochloric  acid  is  as  follows  :  — 

CaCO3     +    2HC1    =     CaCl,    +     H2O     +      C  02, 
Calcium  _   Calcium  Carbon 

carbonate  "   chloride  dioxide. 

Its  Properties.  —  Carbon  dioxide  is  a  colorless  gas.  If 
a  lighted  taper  is  plunged  into  it,  the  flame  is  instantly 
extinguished ;  in  this  respect  carbon  dioxide  resembles 
nitrogen.  If  lime-water  is  exposed  to  its  action  it  will 
be  turned  milky :  this  effect  can  not  be  produced  by  other 
gases.  ^ 

Carbon  dioxide  is  much  heavier  than  air ;  its  density  being 
1.524.  To  illustrate  :  let  the  end  of  the  bent  tube  from  the 

bottle  in  which  this  gas  is  made 
be  placed  in  a  jar,  standing  with 
its  open  mouth  upward  In  a 
little  time  a  lighted  taper,  low- 
ered into  the  jar,  is  quenched, 
showing  that  the  jar  is  full  of 
the  gas.  The  gas  remains  in 
the  open  vessel  as  water  would, 
and  just  for  the  same  reason, 
—  it  is  heavier  than  air.  In- 
deed, it  may  be  poured  from  one 
vessel  to  another  like  water :  its 
flow  can  not  be  seen,  but  a  light- 
ed taper  (Fig.  70)  or  lime-water 

will  show  its  presence  in  the  second  vessel  and  its  absence 
from  the  first. 

Carbon  dioxide  may  be  condensed  to  a  liquid  and  even 
to  a  solid  state.  As  steam  when  cooled  becomes  water,  so 
this  gas  when  made  cold  enough  becomes  a  liquid :  the 
temperature  required  is  —78.2°  C.  And  as  by  being  cooled 
still  further  water  is  frozen,  so  carbon  dioxide  may  be 
changed  from  the  liquid  to  the  solid  form.  To  reduce  the 


Fig.  70. 


CHEMISTRY.  155 

temperature  low  enough,  the  liquid  oxide  is  suddenly  exposed 
to  air  at  ordinary  temperature  and  pressure  :  it  evaporates 
so  swiftly  that  the  large  amount  of  heat  taken  up  by  the 
change  from  the  liquid  to  the  gaseous  form,  leaves  the  rest 
of  the  liquid  so  cold  that  it  freezes. 

/  Gases  may  be  liquefied,  not  only  by  cooling  them  :  the  same 
effect  may  be  produced  by  pressure.  Thus  steam,  whose 
temperature  is  kept  up  to  100°  C.,  will  be  changed  to  water 
by  pressure :  so  carbon  dioxide,  by  a  greater  pressure,  may 
be  liquefied.  At  a  temperature  of  0°  C.  this  requires  a 
pressure  of  thirty-six  atmospheres,  equal  to  540  pounds  to 
the  square  inch.  ) 

168.  Solubility.  —  Carbon  dioxide  is  quite  soluble  in 
water.  This  liquid  at  15°  C.  dissolves  its  own  volume  of  the 
gas.  At  lower  temperatures  it  will  dissolve  more,  and  at 
higher  temperatures  less. 

The  quantity  which  water  will  absorb,  not  only  depends 
on  its  temperature,  but  also  on  the  pressure  to  which  it 
is  subjected.  If  under  twice  the  pressure  of  the  at- 
mosphere, the  quantity  of  gas  dissolved  is  doubled ;  and 
in  all  cases  the  quantity  of  carbon  dioxide  dissolved  by 
water  will  be  directly  proportional  to  the  pressure  upon 
it. 

Soda  Water.  —  The  refreshing  summer  drink  known  as 
"  soda-water  "  is  nothing  but  common  water  holding  carbon 
dioxide  in  solution.  The  violent  foaming  of  soda-water, 
when  drawn  from  the  "fountain,"  is  due  to  the  escape  of 
carbon  dioxide  gas,  which  it  has  been  made  to  dissolve  by 
high  pressure,  but  which  it  can  not  hold  when  under  only  the 
pressure  of  the  atmosphere. 

Water  so  highly  charged  with  carbon  dioxide  is  sometimes 
also  called  seltzer  water.  The  true  seltzer  water  comes  from 
the  celebrated  spring  of  this  name,  and  contains  in  solution 
many  other  things  beside  carbon  dioxide.  The  artificial 
waters  are  greatly  inferior  to  the  natural  waters,  which  are 


156  CHEMISTRY. 

found,  as  at  Saratoga,  in  such  abundance.     Yet  they  are 
wholesome  and  everywhere  highly  esteemed. 

169.  Carbon  Dioxide   and  Respiration.  —  The   pres 
ence  of  this  gas  in  any  considerable  proportion  is  injurious  tc 
animals  breathing  it ;  and,  in  sufficient  quantities,  it  produces 
death   by  suffocation.     It   is,   however,   generally   admitted 
that  the  gas  does  not  possess  the  poisonous  character  once 
attributed  to  it.     It  is  given  off  in  the  breath  ;   and  the  air  in 
unventilated  rooms  quickly  becomes  charged  with  it,   and 
unfit  for  respiration.     Still  the  unpleasant  odor  of  such  air, 
and  its  poisonous  effects  when  breathed,  are  believed  to  be 
due  to  other  gases  furnished  by  the  breath,  rather  than  to 
carbon  dioxide. 

Test  for  its  Presence.  —  This  gas  is  so  heavy  that  it 
is  likely  to  accumulate  in  wells,  in  cellars,  and  in  coal-pits. 
Indeed,  it  is  often  found  in  coal-mines :  the  miners  call  it 
choke-damp.  Before  entering  a  place  where  its  presence  may 
be  suspected,  let  a  lighted  candle  be  introduced.  If  the 
candle  continues  to  burn,  the  air  is  pure  enough  to  be 
breathed  ;  but  if  the  flame  is  extinguished,  life  would  be  also. 

170.  Carbonic  Acid.  —  Carbon  dioxide  is  an  anhydride. 
With  water  it  combines,  and  forms  carbonic  acid,  H2  C  O3. 

C02  +  H20  =  H2C03. 

This  acid  can  not  be  obtained  pure  and  free  ;  but  its  pres- 
ence in  water,  which  has  dissolved  C  O2,  is  demonstrated  by 
adding  a  little  blue  litmus  solution,  which  becomes  red. 

IV.  —  THE  GROUP. 

171.  The   Quadrivalent  Group.  —  Carbon   and  silicon 
are  the  two  quadrivalent  non-metals.     One  atom  of  carbon 
can  hold  four  of  hydrogen  in  combination ;  one  of  silicon 
can  do   the  same.     The   symbols  of  these   compounds  are 
C  H4  and  Si  H4.     Carbon  forms  a  host  of  other  compounds 
with  hydrogen,  some  of  which  will  be  noticed  in  due  time. 


CHEMISTRY.  157 

Other  Properties.  —  These  two  elements  have  each 
three  allotropic  forms.  The  common  form  of  carbon  is 
charcoal :  its  crystalline  forms  are  graphite  and  the  diamond. 
So  the  common  form  of  silicon  is  a  dark-colored  solid,  which 
may  be  changed  to  two  crystalline  forms,  like  graphite  and 
diamond. 

Both  these  elements  are  very  hard,  very  infusible,  and 
able  to  resist  the  action  of  chemicals  in  greater  degree  than 
most  others. 

The  compounds  of  carbon  are  especially  numerous  among 
organic  substances,  while  those  of  silicon  are  to  be  found 
almost  wholly  among  minerals. 

REVIEW. 
I.  — SUMMARY   OP  PRINCIPLES. 

172.  Silicon  and  carbon  are  the  only  quadrivalent  non- 
metals. 

Each  exists  in  three  allotropic  forms. 

Silica  is  the  compound  of  silicon  with  oxygen,  represented 
by  the  formula  Si  O2.  It  is  very  abundant  in  the  earth. 

Silicic  acid  is  represented  by  H2  Si  O3.  The  salts  of  this 
acid  are  silicates,  and  are  very  numerous. 

Glass  is  a  silicate  containing  two  or  more  metals.  It  is 
made  by  melting  together  silica  and  such  bases  as  soda, 
potash,  and  lime.  The  character  of  the  glass  depends  on 
the  bases  used. 

Carbon  is  found  in  the  form  of  coal,  of  diamond,  and  of 
graphite. 

With  oxygen,  carbon  forms  two  oxides,  carbon  oxide  or 
monoxide,  and  carbon  dioxide.  They  are  represented  by 
C  O  and  C  O2. 

Carbon  oxide  is  a  colorless,  combustible,  and  very  poison- 
ous gas. 

Carbon  dioxide  is  also  colorless,  but  not  combustible.  It 
does  not  support  respiration. 


158  CHEMISTRY. 

It  may  be  obtained  by  the  action  of  any  strong  acid  upon 
a  carbonate.  Hydrochloric  acid  and  marble  are  conveniently 
chosen. 

This  gas  is  soluble  in  water,  the  quantity  depending  on  the 
temperature  and  the  pressure. 

The  presence  of  carbon  dioxide  may  be  determined  in  wells 
and  mines  by  means  of  a  candle-flame,  which  it  will  extin- 
guish. 

The  test  used  by  chemists  is  lime-water,  which  the  gas 
renders  milky. 

Carbonic  acid  is  represented  by  H2  C  O3.  The  salts  of  this 
acid  are  the  carbonates,  and  are  very  abundant  in  nature. 
They  are  among  the  useful  substances  in  the  laboratory  also, 
and  in  many  arts. 

II.  —  EXERCISES. 

Describe  the  element  silicon. 

What  is  silica  ?  Where  is  it  found  ?  What  is  silicic  acid  ? 
What  are  silicates  ? 

From  what  is  glass  made  ?  Give  a  brief  description  of  the 
process. 

Describe  the  materials  used  in  making  glass. 

Name  four  varieties  of  glass.  Of  what  different  materials 
are  they  made  ? 

Describe  the  process  of  melting. 

Of  blowing.     Tell  how  a  pane  of  glass  is  made. 

Describe  the  process  of  annealing. 

How  many  ways  of  making  charcoal  are  given  ?  Describe 
the  first.  The  second. 

What  is  said  of  the  abundance  of  carbon  ? 

What  properties  make  the  diamond  so  valuable  ?  What  is 
said  of  its  occurrence  ?  In  what  two  forms  is  it  cut  ?  What 
is  a  carat?  Mention  a  few  of  the  largest  diamonds. 

What  is  said  of  graphite  ? 

Name  the  three  allotropic  forms  of  carbon.  How  do  they 
differ  ?  In  what  respects  are  they  alike  ? 


CHEMISTRY.  159 

Name  the  compounds  of  carbon  and  oxygen.  Give  the 
formula  for  each. 

Describe  carbon  oxide  briefly. 

Of  what  is  carbon  dioxide  composed? 

How  may  this  gas  be  obtained? 

In  what  respects  does  it  resemble  other  gases  ?  In  what 
action  does  it  differ  from  all  others  ?  How  may  we  show  it  to 
be  heavier  than  air?  How  can  this  substance  be  obtained  in 
a  liquid  state?  In  a  solid  state?  What  is  the  effect  when 
this  gas  is  breathed  ? 

What  is  carbonic  acid  ? 

What  is  the  quantivalence  of  silicon  and  of  carbon  ?  How 
are  these  elements  related  by  other  properties? 


SECTION   VII. 

COMBUSTION. 

1. — NATURE  AND  PRODUCTS  OF  COMBUSTION. 

173.  Combustion.  —  Combustion  is  a  mutual  chemical 
action,  generally  between  oxygen  and  some  other  substance, 
and  which,  when  rapid 
enough,  evolves  heat  and 
light. 

When  a  substance  will 
burn  in  air,  it  is  said  to  be 
combustible :  the  air  at  the 
same  time  is  said  to  be  the 
supporter  of  combustion. 
But  really  there  is  no  dif- 
ference in  the  part  played 
by  the  two  things  in  the 
action  :  the  chemical  change  is  mutual. 

Illustrated   by   Experiments.  —  Experiments    may   be 
*«ade  to   illustrate   this    fact.     Fig.  71  represents  a   jar  of 


160 


CHEMISTRY. 


oxygen,  with,  a  jet  of  hydrogen  burning  in  it.  It  is  the 
hydrogen  which  appears  to  burn.  In  Fig.  72  oxygen  is  flow- 
ing from  a  jet,  and  burning  in  a  vessel  kept  full  of  hydro- 
gen :  in  this  case  the  oxygen  appears  to  burn.  The  truth 
is,  that  in  both  cases  alike  the  two  gases  are  combining 
to  form  the  liquid  water. 

Take  an  alcohol  lamp,  and,  by  spreading  its  wick,  make  a 
large  flame.  The  center  of  this  flame  is  dark,  and  is  filled 

with  the  vapor  of  al- 
cohol. Let  the  oxy- 
gen in  a  gas-bag  be 
forced  out  by  a  very 
gentle  pressure,  and 
while  it  is  thus  flow- 
ing in  a  gentle  stream 
let  the  end  of  the 
jet-pipe  be  slowly 
pushed  into  the  edge 
of  the  dark  center  of 
the  alcohol  flame. 
The  jet  of  oxygen 
will  take  fire  while 
entering  the  flame, 
and  then  continue  to 
burn  with  a  very  dis- 
tinct and  pretty  light.  In  this  little  flame  the  oxygen  seems 
to  be  the  combustible,  and  the  alcohol  vapor  the  supporter ; 
while  in  the  large  flame  around  it  the  alcohol  seems  to  be  the 
combustible,  and  the  oxygen  of  the  air  the  supporter.  The 
fact  is,  both  are  equally  combustible. 

174.  Combustion  is  an  Oxidation.  —  In  all  ordinary 
combustion  oxygen  is  one  of  the  active  substances.  When 
wood  burns  in  air,  it  is  because  the  carbon  and  hydrogen  of 
the  wood  combine  with  the  oxygen  of  the  air.  Few,  indeed, 
are  the  exceptions  to  this  :  the  burning  of  a  wax  taper  in  a 
jar  of  chlorine  is  ouv. 


Pig.  72. 


CHEMISTRY.  161 

The  products  of  combustion  must,  therefore,  be  oxides. 

Evolving'  Light  aucl  Heat.  —  The  evolution  of  light 
and  heat  accompanies  all  familiar  cases  of  burning  ;  but  the 
same  chemical  action,  going  on  more  slowly,  gives  off  heat 
without  light.  An  iron  wire,  when  burned  in  moist  oxygen, 
produces  a  splendid  light,  but  when  allowed  to  slowly  rust  in 
air,  no  light  is  ever  seen.  The  chemical  action  is  the  same 
in  both  cases,  —  oxygen  combines  with  the  iron,  and  they 
form  an  oxide.  Moreover,  to  change  the  iron  to  an  oxide 
takes  the  same  amount  of  oxygen  in  the  two  cases  ;  and, 
still  further,  the  same  aggregate  quantity  of  heat  is  given 
off.  Both  are  cases  of  combustion  ;  the  one  being  rapid,  the 
other  slow. 

The  amount  of  heat  depends  upon  the  amount  of  material 
taking  part  in  the  action :  the  intensity  depends  upon  the 
rapidity  with  which  the  action  goes  on. 

175.  The  Kindling"  Temperature.  —  Thin  shavings  of 
the  dryest  pine  wood,  as  is  well  known,  will  rest  in  air  for 
any  length  of  time  unburned  ;  but  when  heated  by  a  burning 
match  how  quickly  do  they  disappear !  The  match,  by  its 
heat,  simply  raises  the  temperature  of  the  wood  until,  having 
reached  a  certain  point,  the  oxygen  of  the  air  begins  rapidly 
to  combine  with  its  elements.  The  temperature  at  which  a 
substance  begins  to  burn  is  tolerably  constant,  and  it  may 
be  called  its  KINDLING  POINT.  The  kindling  point  varies 
greatly  in  different  substances  :  phosphorus,  for  example,  in- 
flames sometimes  by  the  gentle  heat  of  the  hand  ;  while  sul- 
phur must  be  heated  to  about  560°  F.  before  it  will  take  fire, 
and  ordinary  fuels  to  about  1,000°  F. 

Temperature  kept  up  by  Chemical  Action.  —  But 
let  the  burning  once  begin,  and  the  kindling  point  is  kept  up 
by  the  combustion  itself :  a  match  may  kindle  the  fire  which 
destroys  a  city,  but  if  by  any  means  the  burning  body  can  be 
cooled  below  the  kindling  point  the  fire  is  quenched.  Over 
the  flame  of  a  gas-jet  press  down  a  sheet  of  wire-gauze 


162 


CHEMISTRY. 


(Fig.  73)  :  the  gas  goes  through  the  gauze,  the  flame  does 
not.  The  cold  metal  reduces  the  heat,  cooling  the  gas  below 
its  kindling  point.  The  metal  finally  be- 
comes red-hot,  after  which  the  flame  freely 
passes  it. 

Upon  this  principle  the  ' '  safety-lamp  ' '  is 
made  (Fig.  74).  It  consists  of  a  wire-gauze 
cylinder  completely  enveloping  the  burner  of 
the  lamp.  The  combustible  "fire-damp"  of 
a  mine  may  burn  some  time  inside  the  cylin- 
der, warning  the  miners  of  its  dangerous 
presence,  before  the  cold  meshes  of  the  gauze 
will  allow  the  flame  to  pass  out  and  explode  the  mine. 

176.  The  Composition  of  Fuel.  —  All  fuel  is  of  vege- 
table origin.  That  wood  and  charcoal  are  so,  is  evident ; 
not  less  so  are  all  forms  of  coal  found  in  the 
earth.  They  are  the  remains  of  an  ancient 
vegetable  or  forest  growth,  which,  under  the 
influence  of  heat  and  pressure,  has  at  last 
parted  with  its  oxygen  and  hydrogen,  while 
the  carbon  still  remains.  The  resins,  oils  like 
petroleum,  and  coal-gas,  more  rarely  used  for 
fuel,  are  substances  which  have  also  come 
from  the  decomposition  of  plants.  But  all 
these  substances  are  compounds  of  carbon  and 
hydrogen  in  different  proportions.  In  all  or- 
dinary fuels,  carbon  and  hydrogen  are  the  chief 
constituents. 

The  Products  of  Combustion.  —  Upon 
the  bottom  of  a  plate  or  pan  stand  a  burning 
wax  taper,  and  cover  it  with  a  glass  jar  (Fig. 
75).  The  flame  soon  grows  dim,  and  is  finally  extinguished. 
Let  the  taper  be  removed,  and  a  small  quantity  of  lime-water 
poured  into  the  jar.  The  milkiuess  of  the  fluid  shows  the 
presence  of  Qarlton  dioxide.  The  carbon  of  the  wax  has 


Fig.  74. 


CHEMISTRY. 


163 


united  with  the  oxygen  of  the  air,  and  carbon  dioxide  is  a 
product  of  the  combustion. 

Again,  over  the  flame  of  a  burning  gas-jet  hold  a  cold 
glass  jar.  The  sides  of  the  jar  are  quickly  dimmed  with 
dew,  which  must  have  been 
formed  by  the  hydrogen  of  the 
gas  uniting  with  the  oxygen  of 
the  air. 

Water  and  carbon  dioxide  are 
the  important  products  of  all 
ordinary  combustions. 

177.  Gases  only  burn  with 
Flame.  —  The  flames  which  ac- 
company the  combustion  of 
most  substances  are  due  to 

burning  gases.  The  flame  of  a  candle  is  as  truly  a  gas 
flame  as  is  the  flame  of  a  jet  of  illuminating  gas.  The 
solid  wax  or  tallow  in  the  wick  must  be  first  melted  and  then 
vaporized  by  the  heat  of  the  match  before  it  will  take  fire. 
The  gas  once  lighted  causes  a  flame,  whose 
heat  melts  the  wax  below  ;  and  the  liquid, 
lifted  by  capillary  force  through  the  wick, 
is  changed  to  vapor  as  fast  as  it  is  needed 
in  the  flame.  Take  the  wax  in  a  test-tube 
with  a  jet-pipe  through  its  tight  cork,  and 
heat  it.  The  wax  melts,  then  boils,  and 
the  vapor  at  length  issues  from  the  jet, 
when,  if  touched  with  a  lighted  match,  it 
burns  (Fig.  76)  with  exactly  the  same  kind 
of  flame,  only  less  steady. 

Alcohol  and  oil  burn  with  flame  only  after 
heat  has  changed  them  to  vapors.  Bitumi- 
nous coal  and  wood  burn  with  flame  because 
they  contain  substances  which  the  heat  applied  can  vaporize  ; 
while  hard  coal  burns  with  no  flame,  because  it  gives  off  uo 
gases  when  heated. 


Fig.  76. 


164 


CHEMISTRY. 


The  fine  blue  flame  which  is  often  seen  over  an  anthracite 
fire  has  been  already  explained  as  due,  not  to  the  combustion 
of  the  coal,  but  to  the  combustion  of  carbon  oxide.  The 
carbon  at  first  takes  oxygen,  and  becomes  carbon  oxide  ;  and 
then  this  gas,  coming  in  contact  with  oxygen  at  the  surface 
of  the  fire,  combines  with  additional  oxygen,  and  becomes 
carbon  dioxide. 

CO  +  O  =  C02. 

This  combustion  of  the  gas,  C  O,  yields  the  blue  flame. 

178.  Three  Parts  to  a  Common  Flame.  —  The  dark 
center  and  the  luminous  cone  of  common  flames  have  been 
noticed  by  us  all.  This  dark  center  or 
nucleus  consists  of  the  gases  formed  from 
the  fuel ;  but  they  are  not  in  a  burning 
condition.  The  luminous  envelope  consists 
of  these  gases  combining  with  the  oxygen 
of  the  air.  In  this  part  of  the  flame  only 
does  combustion  occur.  Outside  of  this,  is 
an  envelope  made  up  of  water-vapor  and 
carbon  dioxide  produced  by  the  burning. 

The  three  parts  may  be  easily  seen  in  a 
common  candle  flame  (Fig.  77). 

The  nucleus  is  not  burning :  for  the  end 
of  a  match,  plunged  to  the  center  of  the 
flame,  does  not  burn  while  there ;  it  takes 
fire  while  coming  out.  And  even  gunpow- 
der may  rest  in  this  center  of  a  flame  un- 
harmed !  This  can  be  easily  proved.  For 
this  purpose  invert  a  dinner-plate  or  com- 
mon bowl  upon  the  table :  its  bottom  is  a 
very  shallow  dish  which  will  hold  a  small 
quantity  of  alcohol.  Put  some  gunpowder  on  the  end  of  a 
small  cork,  and  place  it  at  the  middle  of  the  plate,  and  then 
touch  the  alcohol  with  a  match.  A  large  flame  is  formed,  in 
the  center  of  which  the  powder  remains  unburned  (Fig.  78) , 


Fig.  77. 


CHEMISTEY. 


165 


until  some  air-current  wafts  the  flame,  or  until  the  alcohol  is 
nearly  consumed. 

The  burning  takes  place  in  the  luminous  envelope.  We 
are  taught  this  by  the  fol- 
lowing experiment :  over  the 
flame  of  an  alcohol-lamp 
suddenly  lower  a  sheet  of 
writing-paper,  holding  it  for 
a  moment  across  the  middle 
of  the  flame  (Fig.  79).  Re- 
move it,  and  a  scorched  ring 
will  be  seen ;  the  paper  is 
burned  just  where  it  was  in 
contact  with  the  luminous 
envelope. 

Hold  a  cold  glass  plate  in  place  of  the  sheet  of  paper  for 
a  moment  on  the  flame  :  a  ring  of  dew  is  condensed  upon  it 
where  it  comes  in  contact  with  the  non-luminous  envelope. 

II.  —  LIGHT  AND  HEAT. 


Fig.  78. 


179.  The    Practical    Value 


Fig.  79. 


of  Combustion.  —  Most 
chemical  processes  are 
valuable  on  account  of 
their  products  ;  but  the 
products  of  combustion, 
water  and  carbon  diox- 
ide, are  of  no  practical 
value  as  products,  and 
combustion  is  never  re- 
sorted to  for  their  sake. 
This  process  is  useful 


simply  for  the  light  and  heat  which  accompany  it. 

180.  Conditions  for  Production  of  Light.  —  Witness 
the  following  experiments.  Let  a  glass  jar  be  inverted  over 
a  burning  taper  (Fig.  80) .  The  flame  continues  for  a  time, 


166 


CHEMISTRY. 


Fig.  80. 


and  then  dies.     It  goes  out  because  its  supply  of  oxygen  is 

exhausted.  Nor  does  it  help  the  matter  much  to  raise  the 
jar  a  little  space  above  the  plate  on 
which  the  taper  stands,  for  the  jar 
remains  full  of  impure  air  which 
keeps  the  pure  air  out. 

Now  again,  put  the  taper  at  the 
bottom  of  a  jar  whose  open  mouth 
is  upward,  and,  if  necessary,  partly 
cover  it  (Fig.  81).  The  flame  dies 
almost  as  quickly  as  before,  and  for 
the  same  reason.  We  learn  from 
these  experiments  that  a  supply  of 
fresh  air  is  absolutely  needed  for 
combustion. 
A  Full  Supply.  —  Go  further :  take  a  lamp-chimney, 

and  so  place  it  that  a  very  small  opening  admits  air  at  the 

bottom  :  the  flame  does  not  die,  but 

burns  dimly.    And  now,  again,  almost 

cover  the  top  of  the  chimney,  leaving 

the  bottom  open  :  the  taper  burns,  but 

with  a  dim  or  smoky  flame.     Finally, 

open  both  top  and  bottom.     A  cur- 
rent of  air  passes  freely  up  through 

the  chimney,   and  we  see  the   taper 

burning  brightly.     These  experiments 

teach   us   that   a  full   supply  of    air 

is  necessary  to  produce   a   luminous 

flame. 

To  the  Surface  of  the  Flame.  —  But  it  will  not  do  to 

mix  the  air  with  the  combustible  gas  :  such  a  mixture  burns 

with  an  almost  lightless  flame. 

This  effect  is  shown  in  the  Bunsen's  burner  (Fig.  82). 

The  gas  is  brought  from  the  chandelier  by  means  of  the 

rubber  tube,  and  issues  from  a  jet-pipe  inside  the  tube  A. 

Just   below   the   end   of    this  jet   are   two   large    holes    on 


Fig.  81. 


CHEMISTRY.  167 

Opposite  sides  of  the  tube,  one  of  which  is  shown  at  6.     A 

movable  collar  c,  with  corresponding  holes,  may  be  turned 

around   the   tube   so   as   to   open  and 

close   these   holes    at    pleasure.     Now 

a  constant  supply  of  gas  from  the  jet, 

and  of  air  entering  at  the  holes,  keeps 

the  tube  (A)  full  of  a  mixture,  which 

is  lighted  as  it  issues  from  the  upper 

end.     This   burning   mixture  gives  an 

intense   heat,  —  a   glass   tube  may  be 

quickly  softened  or  melted  by  it ;  but 

the  light  is  very  feeble. 

The  instrument  is  much  used  in  the 
laboratory   for    heating   glass   vessels, 
for  which  it  is  well  adapted,  because   its   flame  is  without 
smoke  and  deposits  no  soot. 

A  full  supply  of  air  must  be  brought  in  contact  with  the 
surface  of  the  gas-jet  if  the  greatest  light  is  to  be  obtained. 

This  is  clone  in  the  Common  Lamp.  —  The  oil  or 
kerosene  lamp  is  too  familiar  to  need  description.  Notice 
that  the  flat  wick  usually  employed,  exposes  a  large  surface 
to  the  air,  and  that  the  chimney,  open  at  the  top  and  bottom, 
allows  a  constant  current  of  fresh  air  to  pass  up  through  it. 
By  this  means  an  abundance  of  air  is  brought  in  contact 
with  the  flame,  at  its  surface  only,  and  the  bright  light  is  the 
result. 

The  Argand  Burner.  —  In  the  argand  burner  an  artifice 
is  resorted  to,  by  which  the  surface  of  the  flame  exposed  to 
air  is  increased.  The  wick  is  a  hollow  cylinder,  and  the  air 
passes  up  through  the  inside  of  it  as  well  as  around  its  out- 
side. The  gases  from  the  wick  expose  a  double  surface  to 
the  air,  and  give  off  a  greater  light  accordingly. 

The  Gas  Burner.- — The  burner  of  a  gas-chandelier  is 
so  made  that  the  gas  escapes  in  a  fan-shaped  jet.  This  is 
done  in  many  ways.  In  the  end  of  some  burners  we  may 
notice  two  small  holes  ;  and  by  putting  pins  into  these  we 


168  CHEMISTRY. 

find  them  to  be  the  ends  of  two  little  tubes  slanting  toward 
each  other,  so  that  if  continued  outward  they  would  meet. 
Now,  the  two  jets  of  gas  from  these  tubes  strike  against 
each  other  with  force  enough  to  flatten  both  out  into  a  single 
fan-shaped  jet.  In  this  way  a  large  surface  of  gas  is 
exposed  to  air  without  making  a  mixture  of  the  two  sub- 
stances, and  the  luminous  flame  is  produced. 

181.  Source  of  the  Light.  —  Sift  some  finely-powdered 
charcoal  into  the  almost  non-luminous  flame  of  a  Bunsen's 
burner,  and  we  find  that  the  flame  becomes  more  or  less 
luminous.  What  happens  is  this :  The  small  particles  in 
the  hot  flame  are  heated  to  whiteness,  and  shine  with  a  bright 
light.  The  light  quickly  vanishes,  however ;  because  when 
these  hot  particles  of  carbon  come  in  contact  with  air,  they 
instantly  combine  with  oxygen,  and  become  carbon  dioxide. 
The  light  is  due,  while  it  lasts,  to  the  intensely  heated  solid 
particles. 

Doubtless  on  this  principle  we  may.  in  part,  account  for 
the  light  of  common  flames.  We  know  that  the  burning  gas 
is  being  decomposed,  and  that  one  of  its  constituents  is 
carbon.  We  know,  too,  that  carbon  is  a  solid,  even  at  the 
highest  heat,  but  that  heated  in  air  it  combines  with  oxygen. 
At  the  instant,  then,  when  set  free  from  the  burning  gas, 
and  before  its  union  with  oxygen,  each  little  molecule  of 
carbon  is  heated  white-hot,  and,  shining  brightly,  adds  its 
mite  to  the  light  of  the  flame. 

The  Oxyhydrogen  Light.  —  The  luminous  power  of 
solid  bodies  in  a  heat-flame  is  illustrated  by  the  so-called 
oxyhydrogen  or  lime  light.  It  is  made  by  simply  placing  a 
piece  of  lime  in  the  flame  of  the  oxyhydrogen  blow-pipe. 
(Fig.  84.)  So  very  intense  is  this  light,  that  the  eye  is 
blinded  by  its  direct  rays  ;  and,  used  in  light-houses,  it  has 
been  seen  miles  away  at  sea. 

Observe  now :  lime  remains  solid,  even  in  the  most  intense 
heat  of  the  blow-pipe ;  but  the  burning  mixture  gives  heat 


CHEMISTRY.  169 

enough  to  raise  the  lime  to  a  white  heat,  and  in  this  condition 
it  shines  with  a  blinding  light. 

Light  Due  also  to  Dense  Vapors.  —  But  that  all  the 
light  of  flames  is  not  to  be  explained  in  this  way,  is  seen 
clearly  from  the  fact  that  in  some  of  the  most  dazzling  there 
is  no  substance  present  which  can  remain  solid  at  the  tem- 
perature of  the  flame.  Remember  the  blinding  light  of 
phosphorus  burning  in  oxygen-gas.  "  Now,  phosphoric 
anhydride,  the  product  of  this  combustion,  is  volatile  at  a 
red-heat ;  and  it  is,  therefore,  manifestly  impossible  that  this 
substance  should  exist  in  the  solid  form  at  the  temperature 
of  the  phosphorus  flame,  which  far  transcends  the  melting 
point  of  platinum."  (Dr.  Frank-land.)  Many  other  exam- 
ples of  a  similar  kind  might  be  given.  The  light  of  such 
flames,  and  doubtless  much  of  the  light  of  all  flames,  is  due 
to  intensely  heated  dense  vapors. 

182.  Conditions  for   the   Production  of   Heat.  —  If 

heat  is  the  object  sought  for  in  the  process  of  combustion, 
two  conditions  should  be  fulfilled.  There  should  be  &  proper 
supply  of  air  provided,  and  this  supply  should  be  thoroughly 
mixed  with  the  fuel. 

Object  of  Mixing-  the  Air  and  Fuel.  —  By  mixing 
the  air  with  the  fuel  we  enable  the  combustion  to  take  place 
in  every  part  at  once.  It  is  therefore  more  rapid  and 
complete,  and  the  heat  is  more  intense. 

In  the  common  stove  and  furnace,  for  example,  the  air 
entering  at  the  draught  mixes  very  thoroughly  with  the  fuel ; 
and  the  heat  is  much  more  intense  than  it  would  be  if  the 
two  came  in  contact  only  at  the  surface. 

The  Proper  Supply  of  Air.  —  By  the  proper  supply 
of  air  we  mean  just  so  much  as  is  needed  to  furnish  oxygen 
enough  to  combine  with  all  the  fuel. 

Too  little  air  will  leave  some  of  the  fuel  unburned,  and  heat 
will  be  lost.  Too  much  air  will  cool  the  fire  by  carrying 
away  some  heat  into  the  draught. 


170 


CHEMISTRY. 


To  Calculate  the  Quantity.  —  If  we  know  the  composi- 
tion of  the  fuel,  we  can  then  calculate  the  quantity  of  air 
needed  for  its  combustion.  Suppose,  for  example,  we  have 
ten  liters  of  hydrogen,  and  wish  to  get  the  most  intense  heat 
by  burning  it :  how  much  air  must  we  give  it  ?  We  first  find 
how  much  oxygen  it  requires  to  combine  with  it.  We  know 
that  two  volumes  of  hydrogen  take  one  volume  of  oxygen  to 
form  water.  Hence  our  ten  liters  of  hydrogen  must  have  five 
of  oxygen.  We  next  find  how  much  air  is  required  to  furnish 
the  necessary  oxygen.  We  know  that  oxygen  constitutes 
very  nearly  one-fifth  of  the  air ;  hence  it  will  need  twenty-Jive 
liters  of  air  to  give  the  five  liters  of  oxygen  to  burn  the  ten 
of  hydrogen. 

Whatever  the  composition  of  the  fuel  may  be,  knowing  it 
we  can  calculate  just  how  much  oxygen  will  exactly  oxidize 
all  its  constituents,  and  then  the  quantity  of  ai^  required  to 
furnish  this  amount. 

183.  The  Intensity  of  the  Heat.  —  The    intensity   of 
heat  produced  depends  on  the  rapidity  of  the  combustion. 
c  A  brisk  fire  is  a  hot  fire.     A  smolder- 

ing fire  may  burn  longer,  and  in  the 
end  give  out  as  much  heat,  but  at  no 
time  is  it  able  to  scorch,  consume,  or 
fuse  with  vigor. 

The  Oxy hydrogen  Blow-pipe. 
—  A  mixture  of  hydrogen  and  oxy- 
gen, in  the  right  proportions  to  form 
water,  burns  with  heat  of  surprising 
intensity.  By  means  of  the  oxy hy- 
drogen, or  compound  blow-pipe,  this 
,-,"  flame  may  be  obtained  with  little  dan- 

• •       y          ger   of   explosion.      Notice   Fig.   83, 

Fig<  83*  which  shows  a  section  of  one  form  of 

the  jet,  and  Fig.  84,  which  shows  the  instrument  in  use. 
The  gases  are  stored  in  separate  bags,  or  other  reservoirs. 


CHEMISTRY. 


171 


Hydrogen  passes  from  one  of  these  into  the  larger  or  outside 
tube  of  the  jet,  and  flows  out  at  c;  while  oxygen  from  the 


Fig.  84. 

other  passes  through  the  inside  tube,  and  out  at  the  same 
point.  It  will  be  seen  that  the  two  gases  mix  just  at  the 
point  of  the  jet,  and  that  here  the  combustion  takes  place. 
This  is  called  the  concentric  jet.  In  another  form  the  jet 
contains  no  inner  tube.  The  two  gases  are  brought  into  the 
base  of  the  jet,  where  they  mix,  and  the  mixture  issues  from 
the  tip.  This  is  called  the  mixed  jet. 

The  heating  effects  of  this  flame  are  astonishing.  Zinc 
and  antimony  are  vaporized  by  it.  Iron  and  steel  (Fig.  84) 
burn  in  it  like  thread  in  a  lamp- flame.  Platinum,  and  even 
quartz  and  other  rocky  matter,  may  be  melted  or  softened. 
Only  the  heat  of  the  electric  arc  exceeds  this  in  intensity. 

184.  The  Quantity  of  Heat.  —  It  has  been  proved  by 
numerous  experiments  that  the  quantity  of  heat  evolved  by 
combustion  does  not  depend  on  the  rapidity  of  the  action,  but 
only  on  the  weight  of  the  material  burned.  The  burning  of  a 
pound  of  hydrogen  will  yield  precisely  the  same  amount  of 
heat,  whether  it  burn  swiftly  or  slowly.  A  pound  of  carbon 
will  yield  always  exactly  the  same  quantity  of  heat  when  it 
is  changed  into  carbon  dioxide  by  combustion.  If,  however, 
the  carbon  burns  to  carbon  monoxide,  the  pound  will  yield 
less,  because  the  quantity  of  oxygen  burned  is  less.  The 
general  principle  may  be  stated  as  follows  :  — 


172  CHEMISTRY. 

The  same  weight  of  the  same  substance  will  invariably  yield 
the  same  amount  of  heat  tvhen  the  products  of  combustion  are 
the  same. 

A  slow  fire  will  in  the  end  give  just  as  much  heat  as  a 
brisk  one,  if  the  same  quantity  of  fuel  and  air  are  consumed. 

III.  —  RESPIRATION. 

185.  Respiration.  —  The  walls  of  the  air-cells  of  the 
lungs  are  covered  with  a  net-work  of  minute  capillary  blood- 
vessels. Into  the  air-cells  successive  portions  of  fresh  air 
enter,  to  be  at  once  thrown  out  again,  while,  at  the  same 
time,  the  impure  blood  of  the  system  is  constantly  coursing 
through  these  vessels.  We  must  consider  what  changes  are 
being  made,  first  in  the  air,  and  second  in  the  blood. 

The  Chemical  Changes.  —  If  one  breathes  through 
a  tube  into  a  vessel  of  lime-water,  its  milky  color  soon 
shows  the  presence  of  carbon  dioxide.  If  he  breathe  on  a 
cold  surface,  the  moisture  condensed  there  shows  the  pres- 
ence of  water-vapor.  To  determine  what  other  substance 
is  exhaled,  we  may  make  an  experiment,  which  is  repre- 


Fig.  85. 

sented  in  Fig.  85.     A  bell- jar  is  placed  with  its  open  mouth 
in  a  vessel  of  water.     The  jar  is  provided  with  a   cork, 


CHEMISTRY.  173 

through  which  passes  a  tube  which  joins  it  to  the  bottom  of 
a  tall  jar  containing  caustic  potash,  K  H  O.  The  top  of  this 
potash  jar  is  also  provided  with  a  tube  terminating  with  a 
mouth-piece.  Applying  the  lips  to  this  mouth-piece,  the  air 
in  the  jar  may  be  drawn  into  the  lungs,  and  then  returned  to 
the  jar.  Let  this  be  done  two  or  three  times.  In  going 
back  and  forth  between  the  jar  and  the  lips,  the  air  must 
pass  over  the  caustic  potash,  which  will  effectually  remove 
from  it,  both  the  water- vapor  and  the  carbon  dioxide.  Let 
the  flame  of  a  taper  be  afterward  plunged  into  the  jar,  and 
it  will  be  extinguished,  showing  the  absence  of  oxygen  and 
the  presence  of  nitrogen. 

From  all  these  experiments  we  conclude  that  the  air  while 
in  the  lungs  gives  up  its  oxygen,  and  receives  carbon  dioxide 
and  water- vapor. 

Could  we  examine  the  blood,  we  should  find  that  while  in 
the  lungs  its  color  changes  from  purple  to  bright  red,  due  to 
the  loss  of  carbon  dioxide  and  water-vapor,  and  the  receipt 
of  oxygen. 

A  Process  of  Slow  Combustion.  —  Now,  how  can 
these  changes  be  explained?  It  has  been  found  that 
particles  of  the  body  itself  are  constantly  being  worn  out. 
Not  an  act  can  be  done,  a  word  spoken,  nor  can  a  thought 
occur,  without  the  disintegration  of  some  portion  of  the 
organs.  These  waste  particles  are  in  great  part  thrown  into 
the  blood  :  they  are  its  impurities.  These  particles  are  com- 
posed chiefly  of  carbon  and  hydrogen.  The  pure  blood  is 
charged  with  oxygen  ;  and,  as  it  flows,  this  gas  combines  with 
the  carbon  and  hydrogen  of  the  waste,  at  all  points  in  its 
course  ;  and  the  carbon  dioxide  and  water- vapor,  thus  formed, 
pass  into  the  lung-cells,  to  be  finally  exhaled  from  the  system. 
The  action  is  a  process  of  slow  combustion.  The  waste  par- 
ticles are  the  fuel,  oxygen  is  supplied,  and  carbon  dioxide 
and  water- vapor  are  the  products. 

Moreover,  it  is  by  the  heat  evolved  in  this  combustion  that 
the  body  is  kept  warm. 


174  CHEMISTRY. 

Large  Quantities  of  Air  Spoiled.  —  It  will  be  at  once 
seen  that  the  air  of  our  rooms  is  being  constantly  made  unfit 
to  keep  up  this  action  by  which  the  blood  is  purified.  In  the 
first  place,  its  oxygen  is  being  taken  out ;  and,  in  the  second 
place,  impurities  are  being  thrown  into  it.  Not  only  does  it 
receive  the  worn-out  matter  of  the  system  from  the  breath, 
but  we  may  here  add  that  other  portions  of  waste,  even  more 
offensive,  are  incessantly  being  given  into  it  from  the  body 
by  perspiration.  The  total  amount  of  impurity  thus  added 
to  the  air  of  a  close  room  is  frightful ;  since,  upon  the  aver- 
age, about  twenty  thousand  cubic  inches  of  air  pass  through 
the  lungs  of  a  single  person  every  hour ! 

Hence  the  Need  of  Ventilation.  —  As  the  flame  of  a 
taper  dies  in  a  closed  jar,  so  a  human  being  would  die  if 
confined  long  enough  in  an  air-tight  room.  As  the  flame 
flickers  and  burns  dim  when  a  small  supply  of  air  is  fur- 
nished, or  the  products  of  combustion  are  not  removed,  so 
the  life  of  human  beings  flickers  and  grows  feeble  in  rooms 
where  fresh  air  is  not  supplied. 

IV.  —  DECAY. 

186.  Decay.  —  The  decay  of  wood  or  other  vegetable 
matter  is  a  slow  process  of  combustion.  By  the  gradual  loss 
of  carbon  dioxide  and  water,  the  decaying  wood  is  finally 
changed  into  a  brown  or  black  mold,  to  which  the  name 
humus  is  given. 

The  Decay  of  Wood.  —  If  fine  sawdust  is  thoroughly 
moistened,  and  put  into  a  stoppered  bottle  containing  air,  and 
afterward  exposed  to  a  temperature  of  about  16°  C.  (60°  F), 
it  will,  after  a  long  time,  be  found  partially  decayed.  By 
the  usual  tests  it  will  be  found  that  the  air  in  the  bottle  has 
given  up  a  part  of  its  oxygen,  and  received  carbon  dioxide 
in  return. 

Wood,  of  whatever  kind,  when  exposed  to  the  continued 
.action  of  moist  air  and  warmth,  will,  like  the  sawdust  in  the 
experiment,  be  gradually  decomposed.  Moisture  and  warmth 


CHEMISTRY. 


175 


Fig.  86. 


are  essential  to  decay ;  since  it  is  found  that  wood,  exposed 
to  the  cold  of  the  arctic  regions,  or  to  the  dry  air  of  Egypt, 
will  remain,  even  for 
centuries,  in  good  con- 
dition. 

Other  Vegetable 
Matter.  — If  a  flask 
(Fig.  86)  partly  filled 
with  peas  and  water  is 
furnished  with  a -bent 
tube  reaching  over  to 
an  inverted  larger  tube 
filled  with  water,  there 
may,  after  a  time,  be  seen  bubbles  of  gas  rising  into  the 
tube.  This  gas,  if  tested,  will  be  found  to  be  carbon  diox- 
ide ;  and  when  the  peas  are  examined  they  will  be  found  to 
be  partially  decayed. 

A  Slow  Combustion.  —  Now,  the  experiments  with  the 
sawdust  and  the  peas  are  simple  illustrations  of  what  occurs 
whenever  any  kind  of  vegetable  matter  is  long  exposed  to 
the  action  of  air  under  the  influence  of  moisture  and  warmth. 
They  are  slowly  decomposed :  a  part  of  their  carbon  and  of 
their  hydrogen  unites  with  oxygen  to  form  carbon  dioxide 
and  water ;  while  the  rest  of  these  elements,  in  combination 
with  oxygen,  remains  in  the  form  of  a  loose,  solid,  black 
mold. 

The  chemical  action  in  the  process  of  decay  is,  clearly, 
very  similar  to  that  of  combustion.  Indeed,  it  differs  from 
combustion,  chiefly  in  being  less  rapid.  Heat  is  evolved  in 
decay  as  in  combustion,  and  from  equal  quantities  of  material 
the  same  amount.  In  some  rare  cases  a  feeble  light  is  also 
given  off  by  decaying  vegetable  matter.  Decay  is  to  be 
considered  as  but  a  process  of  slow  combustion. 

The  combustion  is,  however,  .very  incomplete.  A  large 
part  of  the  carbon,  and  much  of  the  hydrogen,  of  the 
decaying  body,  is  left  unoxidized. 


176  CHEMISTRY. 

Humus.  —  The  brown  or  black  mold  that  is  left  after  the 
decay  of  plants  is  called  HUMUS.  This  term,  however,  is 
not  the  name  of  a  single  substance,  but  rather  of  a  mixture 
of  several  compounds  of  carbon,  hydrogen,  and  oxygen  in 
various  proportions.  Humus  gives  to  fertile  soils  their  rich 
brown  or  black  appearance. 

REVIEW. 
I.  — SUMMARY  OF  PRINCIPLES. 

187.  Combustion  is  a  mutual  chemical  action,  generally 
between  oxygen  and  some  other  substance,  and  which,  when 
rapid  enough,  evolves  heat  and  light. 

A  certain  temperature  must  be  reached  before  a  substance 
will  kindle ;  but  once  started,  the  chemical  action  will  pro- 
duce heat  enough  to  keep  the  action  going. 

Every  combustible  has  a  kindling  point  peculiar  to  itself. 
Phosphoretted  hydrogen  kindles  on  contact  with  air  at  ordi- 
nary temperatures.  When  this  is  the  case,  the  burning  is 
said  to  be  SPONTANEOUS  COMBUSTION.  On  the  other  hand, 
ordinary  fuels  have  a  kindling  point  of  about  1000°  F. 

Flame  is  extinguished  by  being  cooled  below  the  kindling 
point  of  the  substance.  For  this  reason  flames  will  not 
pass  through  small  openings  in  cold  bodies,  as,  for  example, 
the  interstices  in  wire-gauze. 

All  fuel  is  of  vegetable  origin,  and  consists  chiefly  of 
carbon  and  hydrogen. 

Combustion  is  the  oxidation  of  the  elements  of  the  fuel. 

Carbon  dioxide  and  water  are  therefore  the  chief  products 
of  combustion. 

Flame  is  produced  only  by  the  burning  of  gaseous  matter. 
A  solid,  burning  as  such,  yields  a  glow  of  light  but  no  flame. 

Combustion  is  resorted  to  merely  for  the  heat  and  the  light 
it  produces ;  not  as  in  other  chemical  processes,  for  the 
material  which  it  forms. 

To  give  the  greatest  light,  there  should  be  a  full  supply  of 


CHEMISTRY.  177 

air  to  the  surface  of  the  gas-jet,  as  in  the  common  lamp,  the 
argand  burner,  and  ordinary  gas  flames. 

To  give  the  greatest  heat,  the  air  should  be  thoroughly 
mixed  with  the  burning  gas. 

The  proper  supply  of  air  is  that  which  will  furnish  just 
oxygen  enough  to  unite  with  the  elements  of  the  fuel. 

The  quantity  of  heat  depends  on  the  weight  of  the  material 
burned. 

The  intensity  of  the  heat  depends  on  the  rapidity  of  the 
combustion. 

When  the  oxidation  takes  place  so  slowly  that  no  light  is 
evolved,  it  is  described  as  slow  combustion. 

Respiration  is  a  process  of  slow  combustion.  The  waste 
particles  of  the  body  are  the  fuel :  they  are  oxidized  by  the 
oxygen  of  the  air  which  is  absorbed  by  the  blood  in  its 
passage  through  the  lungs :  carbon  dioxide  and  water- vapor 
are  produced  and  exhaled  in  breathing. 

The  heat  of  this  slow  combustion  is  the  natural  heat  of 
the  body. 

The  decay  of  organic  bodies  is  also  an  analogous  process 
of  slow  combustion. 

II.— EXERCISES. 

What  is  combustion  ?  By  what  experiment  is  it  shown  to 
be  a  mutual  action  ? 

Between  what  substances  does  it  occur? 

Do  light  and  heat  always  accompany  combustion?  Illus- 
trate by  the  combustion  of  iron.  Upon  what  does  the  amount 
of  heat  depend  ?  Upon  what,  its  intensity  ? 

Why  do  not  substances  take  fire  when  simply  exposed  to 
air?  What  is  meant  by  the  term,  kindling  temperature? 
Give  examples. 

How  is  the  temperature  kept  up?  Illustrate.  Describe 
the  experiment  with  the  wire-gauze.  What  does  this 
experiment  teach?  What  application  has  been  made  of 
this  principle? 


178  CHEMISTRY. 

Of  what  is  fuel  composed?  What  are  the  chief  products 
of  combustion? 

What  is  the  origin  of  all  fuel  ?  How  can  this  be  true  of 
coal  ?  Of  resins  and  petroleum  ? 

Describe  the  experiment  with  the  wax  taper.  What  does 
it  teach  ?  The  experiment  with  the  gas-jet.  What  does  it 
teach  ? 

Do  solids,  liquids,  or  gases  burn  with  flame?  How  can 
this  be  true  of  the  candle  flame?  Of  alcohol?  Of  wood? 
Of  hard  coal? 

Name  the  three  parts  of  a  common  flame.  Of  what  is 
each  formed?  Prove  that  the  nucleus  is  not  burning.  How 
may  we  learn  that  the  burning  takes  place  in  the  luminous 
envelope  ?  How  can  we  prove  that  there  is  water  in  the  non- 
luminous  envelope? 

For  what  is  combustion  resorted  to  ? 

In  what  way  is  the  greatest  heat  produced? 

Describe  the  Bunsen's  burner.     Explain  its  action. 

Describe  the  oxyhydrogen  blow-pipe.  What  effects  may 
be  produced  by  it? 

To  get  the  greatest  light  from  combustion,  what  is 
necessary  ? 

Describe  the  first  experiment  with  the  burning  taper.  The 
second.  What  do  these  experiments  teach?  Describe  the 
experiments  with  the  lamp-chimney.  What  do  they  teach? 
Should  the  air  and  gas  be  mixed  ? 

How  is  the  full  supply  of  air  in  contact  with  the  surface  of 
the  flame  secured  in  the  common  lamp? 

In  the  argand-burner  ? 

In  the  gas-burner? 

To  what  is  the  light  of  a  flame  due  ? 

Illustrate  by  the  lime-light. 

What  reason  have  we  to  suppose  that  all  the  light  is  not 
due  to  solid  particles?  To  what  is  it,  then,  due? 

What  kind  of  an  action  is  respiration  ? 

By  what  means  are  the  air  and  blood  in  the  lungs  brought 


CHEMISTRY.  179 

in  contact?  How  may  the  presence  of  carbon  dioxide  in 
the  breath  be  proved  ?  Of  water- vapor  ?  How  may  we  prove 
the  absence  of  oxygen  and  the  presence  of  nitrogen  in  the 
breath?  What  change,  then,  occurs  in  the  air  while  in  the 
lungs  ?  What  change  occurs  in  the  blood  there  at  the  same 
time?  Explain  these  changes. 

How,  then,  is  the  air  of  inhabited  rooms  being  spoiled? 
How  much  impurity  is  thus  being  added  to  the  air? 

Why  is  ventilation  absolutely  necessary? 

What  kind  of  a  process  is  decay?  What  change  takes 
place  in  decaying  bodies  ? 

Describe  the  experiment  with  sawdust.  How  do  we  know 
that  moisture  and  warmth  are  necessary  to  cause  decay? 

Describe  the  experiment  with  the  peas. 

What  do  these  experiments  illustrate  ?  In  what  respects 
are  decay  and  combustion  alike  ? 

What  is  left  after  the  decay  of  plants  ? 


180  CHEMISTRY. 


CHAPTER   III. 
THE   COMPOUNDS   OF   CARBON. 


SECTION   I. 

GENERAL  STATEMENTS. 

188.  Organic  Chemistry.  —  The  compounds  of   carbon 
are  more  numerous  than  those  of  all  other  elements  taken 
together.     Many  of  them  are  very  complex  in  composition. 
They  are,  for  the  most  part,   constituents  of,   or  products 
from,  organic  bodies.     For  these  reasons  they  have  usually 
been   studied   by   themselves,    in   what   is    called    ORGANIC 
CHEMISTRY. 

Organic  chemistry  is  now  defined  to  be  the  chemistry  of 
the  carbon  compounds. 

Carbon  Compounds.  —  By  the  carbon  compounds  we 
here  refer  to  compounds  of  carbon  containing  hydrogen. 
These  two  elements  alone  unite  to  form  a  very  large  num- 
ber of  bodies,  which  are  called  HYDROCARBONS. 

Another  very  large  class  contains  carbon  and  hydrogen 
with  oxygen  ;  and  a  smaller  class  contains  a  few  other  ele- 
ments also,  among  which  are  nitrogen  and  sulphur. 

189.  Organized    Bodies.  —  Plants     and     animals     are 
organized   bodies.     Their  bodies   have   been   nourished  and 
enlarged   by   means   of    food    taken    into    and    distributed 
throughout  their  interior.     The  plant,  by  means  of  certain 
organs,  receives  the  sap  into  its  roots,  and  sends  it  to  every 
part.     Every  leaf  and  stem  is  built  of  substance  which  is 
taken  from  this  sap  and  from  the  air.     The  animal  takes  its 


CHEMISTRY.  181 

food,  converts  it  into  blood,  distributes  it  to  the  most  minute 
fibers  throughout,  and  every  part  of  its  body  is  built  from 
material  thus  furnished. 

Every  distinct  part  of  these  bodies  is  also  organized.  The 
leaf,  the  twig,  and  the  tendril  are  organized  bodies  ;  and  so 
are  the  hairs,  the  claws,  and  the  tissues  of  animals. 

Organic  Substances.  —  These  organized  bodies  consist 
almost  entirely  of  the  compounds  of  carbon  and  hydrogen, 
oxygen  and  nitrogen.  Sugar  (C12 H  ^Ou) ,  starch  (C6  H10  O5) , 
and  alcohol  (C2H6O)  are  three  among  the  thousands  of  sub- 
stances which  the  chemist  is  able  to  get  by  decomposing 
organic  bodies.  Such  compounds  may  be  called  ORGANIC 
SUBSTANCES,  in  distinction  from  ORGANIZED  BODIES  from 
which  they  are  obtained. 

Many  of  these  organic  substances  exist  ready  formed  in 
the  organized  body,  but  many  more  do  not.  These  last  are 
produced  only  by  the  decomposition  of  the  organized  tissues. 

190.  Chemistry  deals  only  with  Organic  Sub- 
stances. —  Now,  it  would  seem  that  Nature  has  fixed  a 
barrier,  which  the  chemist  may  aot  pass,  between  organic 
substances  and  the  organized  bodies  which  they  form.  The 
chemist  can,  by  synthesis,  make  a  few  of  the  simplest 
organic  substances,  and  he  has  good  reason  to  believe  that 
even  the  most  complex  are  produced  by  chemical  force, 
governed  by  the  ordinary  laws  of  combination.  But,  on  the 
other  hand,  the  simplest  organized  body,  although  it  consists 
of  the  same  elements,  is  entirely  beyond  his  reach.  He  can 
not  make  a  single  cell.  By  what  chemistry  the  leaf  and  the 
flower  are  made,  he  does  not  know.  His  laboratory  teems 
with  elegant  crystals  whose  growth  he  has  himself  guided ; 
but  his  garden  is  filled  with  still  more  delicate  forms,  the 
secrets  of  whose  chemistry  are  known  only  to  the  Divine 
Chemist  who  made  the  earth  and  the  sun,  and  all  that  they 
contain. 


182 


CHEMISTRY. 


SECTION  II. 

MARSH-GAS  AND  THE  MARSH-GAS  SERIES. 

191.  Marsh-Gas.  —  The  simplest  hydrocarbon  known  is 
marsh-gas  (CH4),  in  which  one  atom  of  carbon  is  united 
with  four  atoms  of  hydrogen. 

This  gas  is  found  in  nature.  It  is  the  principal  part  of 
the  gas  which  escapes  in  bubbles  when  the  muddy  bottom 
of  a  stagnant  pool  is  disturbed. 

It  may  be  collected  by  receiving  these  bubbles  in  an 
inverted  bottle  (Fig.  87). 


Pig.  87. 

In  this  case  marsh-gas  has  been  produced  by  the  decay  of 
dead  leaves,  or  other  organic  matter ;  and  its  name  comes 
from  the  fact  of  its  occurrence  in  such  places.  This  same 
gas  collects  sometimes  in  mines  ;  and,  by  explosions  of  which 
we  have  all  heard,  now  and  then  extinguishes  the  lamps  and 
the  lives  of  the  miners.  On  this  account  it  has  also  been 
called  FIRE-DAMP. 

Properties.  —  Marsh-gas  is  colorless,  and  only  eight 
times  heavier  than  hydrogen,  or  a  little  more  than  half  as 
heavy  as  air  (.558).  It  burns  vigorously,  with  a  bluish 


CHEMISTRY.  183 

flame  which  is  slightly  luminous.  Its  mixture  with  twice 
its  volume  of  oxygen  explodes  with  great  violence. 

Composition.  —  The  composition  of  marsh-gas  is  repre- 
sented by  its  formula,  C  H4.  That  the  molecule  contains 
four  atoms  of  hydrogen,  may  be  proved  in  this  way :  We 
remember  that  a  molecular  volume  is  always  two  :  hence  two 
volumes  represent  a  molecule  of  the  gas.  Now  pass  electric 
sparks  through  two  volumes  of  marsh-gas  :  it  will  be  decom- 
posed, and  will  yield  just  four  volumes  of  hydrogen.  But 
the  atomic  volume  of  hydrogen  is  one,  and  hence  four  vol- 
umes must  represent  four  atoms.  Therefore,  the  molecule  of 
marsh-gas  yields  four  atoms  of  hydrogen. 

Names.  —  Marsh-gas  is  the  old  and  common  name  of  this 
substance ;  but  the  chemist  calls  it  METHANE,  and  at  other 
times  he  calls  it  METHYL  HYDRIDE. 

This  last  name,  methyl  hydride,  is  intended  to  show  that 
the  gas  is  a  binary  compound  of  hydrogen  and  methyl.  If 
we  write  the  formula  C  H3  H  instead  of  C  H4  we  show  what 
that  methyl  is :  it  is  C  H3,  which  with  hydrogen  forms  the 
hydride.  Chemists  have  much  reason  to  suppose  that  the 
molecule,  CH4,  is  made  up  of  two  parts,  viz.,  C  H3  and  H  ; 
and  the  name,  methyl  hydride,  expresses  this  view,  the  name 
of  the  C  H3  being  methyl. 

192.  The  Marsh-Gas  Series.  —  Methane  is  the  simplest 
of  a  large  number  of  compounds,  which  contain  carbon  and 
hydrogen  holding  a  very  curious  relation.  The  relation  is 
this :  each  one  in  the  series  may  be  obtained  by  adding  C  H% 
to  the  one  before  it.  Let  us  start  with  C  H4  in  the  following 
table,  and  illustrate  this  relation  :  — 

C  H4  .     .     .     .  Methane, 

C  H4   -f  C  H2  =  C2  HG  .     .     .     .  Ethane, 

C2H6   +  CH2  =  C3H8  .     .     .     .  Propane, 

C3H8   +  CH2  =  C4H10  .     .     .     .  Butane, 

C4H10  +  CH2  =  C5H12  .     .     .     .  Pentane, 

etc.    +  etc.   =    etc.  ....  etc. 


184  CHEMISTRY. 

All  these  compounds  actually  exist,  and  many  more  whose 
formulas  the  reader  can  make  for  himself  by  continuing  to 
add  C  H2. 

This  series  of  hydrocarbons,  beginning  with  methane,  and 
increasing  in  complexity  by  the  constant  addition  of  C  H2,  is 
called  the  MARSH-GAS  SERIES.  They  are  also  sometimes 
called  the  PAR  AFFIXES. 

Explanation.  —  Carbon  alone  among  the  elements  is  able 
to  form  so  many  hydrogen  compounds.  Chemists  try  as 
follows  to  explain  this  fact :  In  the  first  place,  the  carbon 
atom  is  quadrivalent ;  and,  in  the  second  place,  one  atom  can 
combine  with  another  atom  of  carbon,  and  saturate  one  or 
more  of  its  units  of  quanti valence,  leaving  the  other  units  to 
be  saturated  by  atoms  of  hydrogen.  This  explanation  is 
considered  very  satisfactory. 

Illustration.  —  If  we  write  the  graphic  formula  for  the 
first  one  in  the  series,  it  stands  thus  :  — 

H 

I 
H— C— H CH4,  Methane. 

I 
H 

If,  now,  we  put  two  atoms  of  carbon  together,  we  must 
add  two  atoms  of  hydrogen  in  order  to  saturate  them. 
Thus :  — 

H    H 
I      I 

H— C— C— H C2H6,      Ethane. 

I      I 
H    H 

If,  again,  we  add  a  third  atom  of  carbon,  we  must  add  two 
more  atoms  of  hydrogen  to  give  the  saturated  molecule. 
Thus :  — 

H   H    H 

H— C— C— C— H    .     .     .     .     C3H8,      Propane. 
I     I     I 
H    H    H 


CHEMISTRY.  185 

Thus  we  see,  that,  carbon  remaining  quadrivalent,  and  its 
atoms  combining  together  by  one  unit,  the  constant  addition 
of  C  H2  must  produce  the  successive  members  of  the  series. 

193.  Properties  of  the  Marsh-Gas  Series.  —  The  first 
five  members  of  this  series  are  gases  at  ordinary  tempera- 
tures.    Several  which  follow  are  liquids,  while  from  C^H^ 
onward  in  the  series  the  substances  are  solids. 

Each  one  of  the  liquids  has  its  own  boiling-point.  Pen- 
tane,  for  example,  boils  at  30°  C.,  and  hexane  at  about  60°  C. 
TJie  boiling-point  rises  about  30°  (7.  for  each  addition  of  C  H2. 

The  series  is  remarkably  indifferent  to  nearly  all  chemical 
agents.  Its  members  are  all  combustible,  and  in  other  chemi- 
cal actions  they  exchange  atoms  of  hydrogen  for  atoms  of 
other  elements. 

194.  Petroleum.  —  Petroleum    is    an    oily    liquid   of   a 
greenish  color,  found  in  the  rocks  of  various  parts  of  the 
world.     It  is  especially  abundant  in  Pennsylvania,  where  it 
is  obtained  in  large  quantities  for  commercial  purposes. 

Composition.  —  Petroleum  is  a  mixture  of  hydrocarbons  ; 
and  these  are  chiefly,  but  not  wholly,  of  the  marsh-gas  series. 
All  the  members  of  the  series  from  C4  H10  to  C9  H^  are  present. 

Fractional  Distillation.  —  Since  each  hydrocarbon  has 
its  own  boiling-point,  it  is  possible  to  separate  several,  when 
mixed,  by  distillation.  Let  the  mixture  be  heated  up  to  the 
loivest  boiling-point,  and  kept  steadily  at  that  temperature  ; 
only  the  vapors  of  the  one  substance  having  that  boiling- 
point  will  be  driven  off,  and  these  may  be  condensed  in  a 
receiver.  When  these  vapors  cease  to  flow,  let  the  tempera- 
ture be  raised  up  to  the  next  boiling-point,  and  maintained  : 
only  the  vapors  of  the  substance  having  this  next  higher 
boiling-point  will  be  driven  off,  and  these  may  be  condensed 
in  a  separate  receiver.  Similarly  each  one  in  the  mixture 
may  be  obtained  in  a  separate  vessel.  This  distillation  of  a 
liquid  at  the  successive  boiling-points  of  its  constituents  is 
called  FRACTIONAL  DISTILLATION. 


186  CHEMISTRY. 

For  Commercial  Purposes.  —  Kerosene  oil,  naphtha, 
and  gasoline  are  among  the  products  obtained  from  petro- 
leum for  various  uses  in  the  arts.  None  of  these  are  single 
compounds :  each  is  a  mixture  of  several  hydrocarbons. 
They  are  obtained  from  petroleum  by  fractional  distillation ; 
although  the  temperatures  used  are  not  the  successive  boiling- 
points  of  its  chemical  constituents,  but  are  arbitrarily  chosen 
instead.  On  this  account  each  product  is  a  mixture. 

The  following  table,  from  Wagner's  Chemical  Technology 
(Crookes),  shows  temperatures  used,  and  names  the  commer- 
cial product  obtained :  — 

Below  37.7°  C Rhigoline, 

At        76.6°  "  .     '.'   r.vv- . "v    .  Gasoline, 

At      137.0°  " .  Naphtha, 

At      148.0°  "  .   -.  °::<:  ->  ,:v  • ;     .  Benzine, 

At      183.0°  -  219.0°  C.  .  Kerosene. 


SECTION  III. 

THE  ALCOHOLS. 

195.  Common  Alcohol.  —  When  the  juices  of  fruits 
containing  sugar  are  kept  warm  for  several  hours,  a  peculiar 
change  occurs.  Their  sweetness  becomes  less  and  less ; 
bubbles  of  carbon  dioxide  escape  ;  and,  at  the  same  time, 
alcohol  is  formed  in  the  liquid.  The  chemical  action,  called 
fermentation,  is  to  be  described  more  fully  in  the  future. 

The  alcohol  may  be  separated'  by  distilling  the  liquid  in 
which  it  is  formed ;  its  boiling-point  being  about  85.5°  C. 
(186°  F.). 

But  mere  distillation  from  the  fermented  liquor,  while  it 
may  furnish  a  concentrated  spirit,  can  not  give  one  entirely 
free  from  water.  The  attraction  of  alcohol  for  water  is  so 
strong  that  a  small  portion  will  be  retained  by  it  after  the 
most  careful  distillation.  It  can  be  removed  by  the  stronger 


CHEMISTRY.  187 

attraction  of  quicklime,  and  when  this  is  done  the  product 
is  called  absolute  alcohol ;  but  on  exposure  to  air  it  soon 
absorbs  water  again,  so  that  absolute  alcohol  is  of  rare 
occurrence.  The  specific  gravity  of  absolute  alcohol  is  .794  ; 
of  the  strongest  commercial  alcohol,  which  contains  about 
ten  per  cent  of  water,  it  is  .825. 

Properties.  —  Alcohol  is  a  colorless,  limpid  liquid,  lighter 
than  water.  It  burns  readily  with  a  hot,  but  not  a  bright, 
flame.  It  is  able  to  dissolve  resins  and  oils,  and  many  other 
substances  which  water  can  not ;  and  this  solvent  power 
renders  it  useful  in  the  arts. 

Composition.  —  The  composition  of  alcohol  is  shown  by 
its  formula  C2H6O.  This  is  its  empirical  formula.  It  is 
often  written  also  C2  H5  H  O,  which  represents  the  belief  that 
its  molecule  consists  of  two  groups  of  atoms,  C2H5  and 
HO. 

It  is  interesting  to  know  why  the  chemist  should  feel 
inclined  to  arrange  the  atoms  in  the  molecule  in  these  two 
groups,  and  a  little  attention  will  show  the  reason. 

Constitution  of  the  Molecule.  —  He  finds,  that  if  he 
mixes  ethane,  C2H6,  and  chlorine,  he  may  bring  about  the 
following  reaction :  — 

C2H6    +      2C1      =        C2H5C1        +  HC1, 

Ethane  -f-  Chlorine  =  Ethyl  chloride  -f  Hydrochloric  acid  ; 

and,  if  he  then  treats  the  ethyl  chloride  with  silver  hydrate,  he 
produces  alcohol.  Thus,  — 

C2H5C1   -f  AgHO  =  C2H5HO  +     AgCl, 

Ethyl  Silver  A1     ,    ,  Silver 

chloride  "  hydrate  =  "  chloride. 

Now,  the  C2  H5  seems  to  have  come  along  down  from  the 
ethane  unbroken,  while  the  H  O,  from  the  silver  hydrate,  has 
been  added  to  it ;  and  the  union  of  these  two  groups,  C2H5, 
H  O,  seems  to  give  the  molecule  of  alcohol. 

This  is  only  one  of  the  chemical  actions  which  can  be  best 


188  CHEMISTRY. 

explained  by  this  view  of  the  arrangement  of  atoms  in  the 
molecule  of  alcohol.  It  is  very  generally  accepted. 

Derived  from  Ethane.  —  Compare  C2  H6  with  C>  H5  H  O, 
and  we  see  that  the  latter  would  be  obtained  by  substituting 
H  O  for  H  in  the  former. 

That  is,  alcohol  may  be  derived  from  ethane  by  substituting 
a  molecule  of  hydroxyl  for  one  atom  of  hydrogen.  This  may 
be  clearly  shown  by  the  constitutional  formula :  — 

H    H  H    H 

H— C— C— H  H— C— C— O— H 

A  A  A  A 

Ethane  Alcohol 

where  it  is  seen  that  if  we  only  put  the  two  atoms,  OH,  in 
place  of  the  right-hand  atom  of  hydrogen  in  ethane,  we 
change  the  molecule  of  ethane  into  a  molecule  of  alcohol. 

196.  The  Series  of  Alcohols.  —  Now,  hydroxyl  may  be 
substituted  for  an  atom  of  hydrogen  in  other  members  of  the 
marsh-gas  series  as  well  as  in  ethane. 

Methane,  C  H4 ,  becomes  C  H3  OH, 
Ethane,  C2  H6 ,  "  C2  H5  O  H, 
Propane,  C3  H8 ,  "  C3  H7  O  H, 
Butane,  C4H10,  "  C4H9  OH, 
Pentane,  C^,  "  C5HUOH. 

The  new  compounds  are  all  of  them  ALCOHOLS.  Alcohol 
is,  therefore,  the  name  of  a  large  class  of  bodies,  instead  of 
a  single  compound.  An  alcohol  is  a  substance  derived  from 
a  member  of  the  marsh-gas  series  by  substituting  hydroxyl  for 
hydrogen. 

Their  Names.  —  The  first  in  the  series  is  called  methyl 
alcohol,  from  the  hydrocarbon  group,  CH3,  the  name  of 
which  is  methyl.  The  second  is  called  ethyl  alcohol,  from 
the  group  C8  H5,  or  ethyl.  The  third  is  propyl  alcohol,  from 


CHEMISTRY.  189 

propyl,  C3H7.  In  every  case  the  name  of  the  alcohol  is  the 
name  of  the  hydrocarbon  in  it;  and  the  name  of  the  hydro- 
carbon in  it  is  the  name  of  the  corresponding  member  of  the 
marsh-gas  series  with  the  ending  ane  changed  to  yl. 

197.  Radicals.  —  These  hydrocarbons  in  the  alcohols  are 
called  ALCOHOL  RADICALS.     This  term  radical  is  applied  to 
any  group  of  atoms  which  is  not  broken  up  during  chemical 
changes,  but  which  seems  to  go  bodily  from  one  molecule 
into  another. 

Let  us  take  the  case  of  methane,  C  H4,  and  represent  it  as 
methyl  hydride,  CH3H.  Now,  if  we  mix  chlorine  with  this, 
the  molecule  C  H3  H  will  be  changed  into  C  H3  Cl ;  and  then, 
if  we  treat  this  with  silver  hydrate,  Ag  O  H,  the  molecule 
CH3Clwill  be  changed  into  CH3OH.  We  here  see  that 
the  group  C  H3  remains  unbroken  while  the  substance 
changes.  This  is  what  the  term  radical  implies. 

These  alcohol  radicals  are  all  unsaturated  molecules  with 
one  free  unit  of  quautivalence  :  they  are  univalent. 

SECTION   IV. 

THE  ETHERS. 

198.  Ether.  —  Ether   is    a    transparent    liquid,    with    a 
peculiar   odor,  and   a   sweetish   taste.      When   breathed,  it 
causes  exhilaration  at  first,  but  perfect  insensibility  at  last. 
On   this   account   ether  has   been   used   to   render  patients 
insensible  to  the  pain  of  surgical  operations. 

The  evaporation  of  ether  produces  intense  cold :  a  pretty 
experiment  can  illustrate  this.  Let  a  drop  or  two  of  water 
be  covered  with  a  few  drops  of  ether,  and  by  a  bellows  or  a 
blow-pipe  let  a  current  of  air  be  blown  against  the  ether. 
By  its  rapid  evaporation  the  ether  takes  away  the  heat,  until 
the  water  is  frozen.  A  mixture  of  ether  with  solid  carbon 
dioxide  will  produce  a  temperature  of  —110°  C.  (  —  166°  F.). 
Pure  ether  has  never  been  frozen. 


190  CHEMISTRY. 

Liquid  ether  is  much  lighter  than  water,  but  its  vapor  is 
much  heavier  than  air. 

Ether  is  very  combustible,  burning  with  a  bright  flame  ; 
and  a  mixture  of  its  vapor  with  air  is  explosive. 

Ether  is  used  in  medicine,  and  extensively  by  the  chemist 
as  a  solvent.  Oils  and  resins,  caoutchouc,  and  many  other 
organic  substances,  are  soluble  in  this  liquid.  It  is  a  more 
powerful  solvent  than  alcohol. 

Preparation.  — When  a  mixture  of  concentrated  sulphuric 
acid  and  alcohol  is  heated  to  about  140°  C.,  a  very  volatile 
substance  is  formed,  whose  vapors  may  be  condensed  in  a 
separate  vessel.  It  is  sulphuric  ether;  or,  since  it  is  the  only 
ether  of  commercial  importance,  it  is  called  simply  ETHER. 
The  chemical  change  is  complicated  ;  but  the  result  of  it  all 
is,  that  the  alcohol  is  changed  into  ether  and  water. 

2C2H5OH  =    (C2H5)20  +    H20, 
Alcohol      =       Ether       +  Water. 

Two  molecules  of  alcohol  yield  one  molecule  of  ether  and 
one  of  water. 

199.  The  Series.  —  Just  as  common  or  ethyl  alcohol 
yields  common  ether  when  treated  with  sulphuric  acid,  so 
each  alcohol  will  yield  a  corresponding  ether.  Thus  :  — 

Methyl  alcohol  yields  Methyl  ether, 
Ethyl  alcohol         "      Ethyl  ether, 
Propyl  alcohol       "      Propyl  ether. 

Hence  the  term  ether,  like  alcohol,  is  the  name  of  a  large 
class  of  compounds.  Indeed,  this  series  of  simple  ethers  is 
only  one  of  several  series.  Nitric  acid,  also,  converts  the 
alcohols  into  ethers  ;  and  any  other  strong  acid  will  yield  a 
series  of  compounds  belonging  to  this  same  large  family. 
An  ether  is  a  compound  produced  by  the  action  of  a  strong 
acid  on  an  alcohol. 

We  may  notice  that  common  ether  is  an  oxide   of   the 


CHEMISTRY.  191 

radical  ethyl.  This  is  shown  by  its  formula  (C2H5)2O.  So 
all  this  series  of  ethers  obtained  by  sulphuric  acid  are  oxides 
in  which  one  atom  of  oxygen  is  combined  with  two  molecules 
of  a  radical. 


SECTION  V. 

OLEFIANT  GAS  AND  THE   OLEFINES. 

200.  Olefiant  Gas.  —  Olefiant  gas   is   another  compound 
of  carbon  and  hydrogen,  whose  composition  is  shown  by  the 
formula  C2H4.     It  is  a  colorless   and  very  combustible  gas, 
and  burns  with  a  bright  flame.     It  is  found  in  small  quanti- 
ties in  illuminating  gas,  and  was  formerly  thought  to  be  the 
most  important  constituent  in  it ;  but  this  idea  has  been  aban- 
doned.    Mixed  with  air  it  explodes  violently. 

Olefiant  gas  is  sometimes  called  ETHYLENE,  and  sometimes 
ETHENE. 

201.  The  Olefines.  —  We  have  seen  that  marsh-gas  is  the 
simplest  or  first  member  of  a  long  series  of  hydrocarbons,  in 
which  there  is  a  constant  difference  of  C  H2.     Olefiant  gas  is 
like  marsh-gas  in  this  respect ;  for  it  is  also  the   simplest  or 
first  member  of  a  long  series,  in  which   there   is   a  constant 
difference  of  C  H2.     Thus  we  have 

C2H4  ....  Ethene, 

C2H4  -f  CH2  =  C3H6  .     .     .     .  Propene, 

C3H6  +  CH2  =  C4H8  .     .     .     .  Butene, 

C4H8  +  CH2  =  C5H10  .     .     .     .  Penteue. 

The  members  of   this   series   are   produced   by  distilling 
organic  bodies,  and  they  are  found  also  in  petroleum. 

202.  Homologous  Series.  —  Any  series  of  compounds, 
the  members  of  which  differ  by  the  common  difference,  C  H2, 
is   called   a   HOMOLOGOUS    SERIES.     The  paraffines  and  the 
defines  are  only  two   homologous  series  of   hydrocarbons. : 


192 


CHEMISTRY. 


many  others  are  known,  and  all  together  include  a  multitude 
of  compounds.  The  members  of  each  series  agree  in  cer- 
tain relations  and  properties,  so  that  a  description  of  one  is 
to  some  extent  a  description  of  them  all.  Were  it  not  that 
they  may  be  arranged  in  these  natural  groups,  any  thing  like 
an  exhaustive  study  of  the  hydrocarbons  would  be  an  over- 
whelming task. 


SECTION  VI. 
DESTRUCTIVE  DISTILLATION. 

203.  Destructive  Distillation.  —  When  wood  or  othet^ 
vegetable  substance  is  heated  in  close  vessels,  it  is  decom- 
posed.    The    process   is    called  DESTRUCTIVE   DISTILLATION. 
Some  of  the  products  are  solid,  some  are  liquid,  and  some 
are  gaseous  :  these  three  classes  of   substances  are  always 
produced  by  destructive  distillation. 

204.  Destructive  Distillation  of  Wood.  —  Let  the  fol- 
lowing experiment  be  tried.     Into  a  small  flask   (Fig.  88) 

put  some  fine  splint- 
ers of  some  hard 
wood :  beech-wood 
answers  the  purpose 
well.  Let  the  flask 
be  tightly  corked, 
and  provided  with  a 
bent  tube  reaching 
over  into  a  bottle 
which  is  kept  cold 
by  the  water  which 
surrounds  it.  On 
heating  the  flask  the  wood  soon  turns  black  :  volatile  matter 
is  driven  over,  some  of  it  being  condensed  in  tke  bottle, 
while  another  part  escapes  in  the  form  of  gas.  This  gas 
may  be  collected  in  a  second  bottle  over  water,  by  passing  it 


Fig.  88. 


CHEMISTRY.  193 

through  a  rubber  tube  reaching  from  the  short  tube  t.  The 
black  solid  left  in  the  flask  is  charcoal :  the  gas  collected  is  a 
mixture  of  several,  —  marsh-gas  and  defiant  gas  being  among 
them  ;  while  the  fluid  in  the  first  bottle  consists  of  pyrolig- 
neous  acid  and  wood-tar. 

Charcoal  and  the  gases  have  already  been  described. 

205.  Pyroligneous  Acid.  —  Pyroligneous   acid   is   often 
called  wood-vinegar.     Dry  beech-wood  yields  it  in  greatest 
abundance.     It  is  a  dark-brown  liquid,  with   a  sour,  smoky 
taste.     It  contains  acetic  acid  ;  and  on  this  account  has  been 
largely  used  in  making  such  acetates  as  are  employed  in  the 
arts,  especially  in  calico-printing  and  dyeing.     Sodium  ace- 
tate and  lead  acetate  are  examples. 

206.  Wood-Tar.  —  Wood-tar  is  a  very  dark-colored  resi- 
nous fluid.     There  are  several  varieties.     One,  largely  used 
in  ship-building  and  other  arts,  is  obtained  by  a  rude  distilla- 
tion of  resinous  pine-wood :  another  is  obtained   from  hard 
wood.     It  is  sometimes  used  as  a  covering  for  wood  to  pre- 
serve it  from  decay :  the  more  volatile   constituents  of  the 
tar  passing  away,  leave  the  harder  part  (pitch)   in  the  pores 
of  the  wood.     Water  is  thus   kept  out  of  the  pores  of  the 
wood ;  and  this,  together  with  the   action  of  creosote,  to  be 
soon  noticed,  prevents  decay. 

207.  Methyl  Alcohol.  —  When  pyroligneous  acid  is  dis- 
tilled, a  very  volatile  liquid  may  be  obtained,  which,  being 
afterward  rectified  by  the  use  of  quicklime,  constitutes  the 
METHYL  ALCOHOL  of  commerce.     It  is  a  limpid  liquid,  very 
inflammable.     It  may  be  used  instead  of  alcohol  for  many 
purposes,  especially  for  dissolving  resins  in  making  varnish. 
It  is  the  simplest  member  of  the  alcohol  series. 

208.  Creosote.  —  The  smoky  taste  of  pyroligneous  acid, 
and  the  power  of  both  this  acid  and  wood-tar  to  prevent 
decay,  is  due  to  the  presence  of  a  curious  compound  of  car- 
bon,   hydrogen,    and  oxygen    (C$Hi0O)3    called   CKEOSOTE- 


194  CHEMISTRY. 

One  pound  of  the  acid  contains  about  a  quarter  of  an  ounce 
of  it  in  solution.  Its  most  curious  and  valuable  property  is 
its  power  to  prevent  decay :  indeed,  it  is  among  the  most 
powerful  antiseptics  known.  Flesh  remaining  a  few  hours 
in  a  fluid  made  by  dissolving  one  part  of  creosote  in  one 
hundred  parts  of  water  will  not  afterward  decay.  That 
meats  are  often  cured  by  exposure  to  smoke,  is  familiar  to 
all :  now,  the  preservation  and  the  peculiar  flavor  of  smoked 
meat  is  due  to  the  action  of  creosote  in  the  smoke.  This  sub- 
stance is  often  used  in  medicine  ;  but  when  taken  internally, 
except  in  very  small  quantities,  it  is  a  corrosive  poison. 

209.  Paraffine.  —  Paraffine  may  be  obtained  by  distilling 
wood-tar.     It  is  a  crystalline  solid,  with  neither  taste,  color, 
nor  smell.     Its  most  remarkable  property  is  its  indifference 
to  the  chemical  action  of  other  substances.     It  can  resist  the 
action  of  the  strongest  alkalies  and  of  the  most  corrosive 
acids.     It  is,  however,  combustible,  and  its  flame  is  white 
and  smokeless.     Paraffine  candles  rival  the  most  costly  wax 
candles  in  luster  and   in   the  strength   and  beauty  of  their 
light. 

210.  Other   Substances.  —  Numerous    substances,    be- 
sides   the    few   just    described,    may   be   obtained    by   the 
destructive   distillation   of    wood.     Each   different   kind   of 
wood  and   of  other  vegetable  matter  yields  some  different 
products ;  but  for  the  most  part  they  are  all  compounds  of 
carbon  with  either  hydrogen  or  oxygen,  often  with  both. 

It  should  be  noticed  that  none  of  these  products  are 
supposed  to  exist  ready  formed  in  the  plant.  By  heat  the 
substance  of  the  plant  is  broken  up ;  its  elements  are  re- 
arranged, and  these  hydrocarbons  formed  thereby. 

Application  of  this  Process.  —  Destructive  distillation 
is  used  on  a  large  scale  in  the  manufacture  of  illuminating- 
gas.  In  this  manufacture  the  solid  and  liquid  products  are 
of  secondary  importance,  while  the  gaseous  products  are 
secured  as  pure  as  possible. 


CHEMISTRY. 


195 


Any  complete  apparatus  for  illustrating  the  process  of 
destructive  distillation  illustrates  also  the  essential  parts  of 
the  apparatus  of  the  gas-house.  For  example,  in  Fig.  89, 


Fig.  89. 

there  is  ayfasfc,  in  which  the  organic  matter  is  heated  ;  a  bottle 
surrounded  by  cold  water,  in  which  impurities  are  condensed  ; 
and  a  receiver  over  water,  in  which  the  gas  is  collected. 
These  three  parts  of  the  apparatus  are  represented  in  every 
"  gas-works." 

211.  Manufacture    of    Illuminating   Gas.  —  By    the 

destructive  distillation  of  bituminous  coal,  and  sometimes  of 
other  substances,  illuminating-gas  is  made.  The  material 
being  heated  in  iron  retorts,  its  volatile  constituents  are 
driven  off.  The  gas  thus  formed  is  purified  by  passing  first 
through  cold  pipes,  and  then  over  lime.  It  is  afterward 
collected  in  gas-holders,  from  which  it  is  pressed  out  into 
the  pipes  of  the  city,  and  through  these  into  the  chandeliers 
of  the  houses. 

The  following  is  an  outline  of  this  important  manufacture. 

212.  Bituminous  Coal.  —  In  the   United  States  alone, 
there  are  about  130,000  square  miles  of  workable  coal-fields. 
The  coal  found  so  abundantly  in  nature  is  called  MINERAL 
COAL  :  it  consists  of  carbon  mixed  with  other  matter,  espe- 
cially with  volatile  compounds  of  carbon  and  hydrogen.     The 


196 


CHEMISTRY. 


two  varieties  of  mineral  coal,  anthracite  and  bituminous, 
differ  chiefly  in  the  amount  of  their  volatile  constituents. 
The  first  contains  very  little  of  the  hydrocarbons,  is  very 
hard,  and  burns  with  a  very  feeble  bluish  flame ;  the  second 
contains  a  large  amount  of  volatile  compounds,  is  much 
softer,  and  burns  with  a  bright  flame.  From  bituminous 
coal  illuminating-gas  is  generally  made. 

Heated  in  Iron  Retorts.  —  The  vessels  in  which  the 
coal  is  heated  are  called  retorts.  They  are  usually  of  iron, 
about  seven  feet  long,  and  scarcely  more  than  a  foot  in 
diameter.  Fig.  90  shows  the  ends  of  five  of  these  retorts 

placed  in  a  single 
furnace.  Each  one, 
after  receiving  a 
charge  of  from  one 
hundred  pounds  to 
one  hundred  and  fifty 
pounds,  is  closed  air- 
tight as  shown  at 
G,  and  made  red-hot 
by  the  fire  in  the 
furnace,  whose  doors 
are  shown  at  A.  In 

the  course  of  a  few  hours  the  volatile  matter  of  the  coal  is 
driven  off  :  the  residue,  called  coke,  is  then  raked  out,  cooled, 
and  used  for  fuel. 

Its  Volatile  Constituents.  —  The  gaseous  mixture 
driven  off  by  heat  contains  marsh-gas  and  many  other 
hydrocarbons,  carbon  dioxide,  hydrogen,  ammonia,  hydro- 
sulphuric  acid,  and  coal-tar,  besides  other  substances.  This 
mixture  is  totally  unfit  for  use,  and  must  be  purified. 

Pass  through  the  Hydraulic  Main.  —  From  each 
retort  a  vertical  pipe  (i  i  i,  Fig.  90)  is  an  outlet  for  this 
mixture  of  gases.  This  pipe,  bending  over  at  the  top, 
reaches  down  into  a  larger  and  horizontal  tube  or  trunk,  H, 
called  the  HYDRAULIC  MAIX.  In  the  beginning  of  this  pro- 


CHEMISTRY. 


197 


cess  this  main  is  filled  half  full  of  water,  and  the  pipes  i  i 
dip  into  this  fluid.  The  gas  coming  over  from  the  retorts 
bubbles  up  through  the  water,  which  prevents  its  return. 
Now  the  vapors  of  coal-tar  will  be  condensed,  in  part,  by 
the  lower  temperature  of  the  main  ;  but,  as  the  fluid  increases, 
it  runs  off  through  the  tube  L  to  a  tar-cistern.  Much  of  the 
coal-tar  is  left  in  the  hydraulic  main,  while  the  gas  passes 
out  of  it  through  the  pipe  K. 

Throug-h  the  Condensers.  —  This  pipe,    K,    leads   the 
gases  over  to  a  series  of  upright 
pipes,  CC  (Fig.  91),  called  the 
condensers.    Passing  up  one,  and 
down   another,  until  they   have 
traversed  the  whole  series,   the 
gases   are   exposed    to    a    large 
extent  of  cold  surface,  and  the 
condensable   gases  are  changed 
to  a  liquid  state.     The  tar  and 
ammoniacal     liquor     thus     con 
densed  run  into  a  cistern  below, 
drawn  off  at  pleasure. 

Through  the  Lime  Purifier. 


Fig.  91. 

from  which  they  may  be 


The  gas,  still  contain- 
ing sulphur  compounds  and  carbonic 
acid,  passes    from    the    condensers 
p  through  a  pipe  (L)  into  a  chamber 
(Fig.  92)  in  which  are  several  sieve- 
like  shelves  covered  with  slaked  lime. 
In  passing  through  the  lime  the  gas 
loses  its  carbon  dioxide  and  hydro- 
Figi  92'  sulphuric  acid. 

Into  the  Gasometer.  —  The  purified  gas,  leaving  the 
lime  chamber  through  a  pipe  (P),  passes  into  the  gas-holder 
(Fig.  93),  an  immense  sheet-iron  cylinder,  closed  at  the  top 
and  opened  at  the  bottom,  hung  by  chains  which  run  over 
pulleys  at  the  top,  and  which  carry  weights  to  balance  it. 
Below  it  is  a  well  of  water  large  enough  arid  deep  enough 


198 


CHEMISTRY. 


to  let  this  cylinder  down  until  it  is  filled  with  water.     As 
the  gas  enters  it  the  gas-holder  rises  ;  and,  when  it  is  filled, 

the  gas  is  read}7  to  be  pushed 
out  through  the  pipe  S  into 
the  streets,  and  finally  into 
the  houses  of  the  city,  fur- 
nishing to  all  a  convenient 
and  beautiful  light. 

"In  the  iron  arteries  under 
towns,  in  the  constellations 
of  burners  that  rule  the  nights 
of  favored  days,  rising  over 
the  chaotic  oil-lamps  of  old, 
what  a  creation  !  " 


Pig.  93. 


213.  Gas  from  Petrole- 
um. —  A  very  elegant  and 
successful  process  of  making  gas  from  petroleum  has  in 
recent  years  been  successfully  carried  out.  In  this  process 
petroleum  vapor  and  water-gas  are  brought  together  in  a 
white-hot  retort,  from  which  they  issue  as  a  mixture  of  per- 
manent gases  of  good  illuminating  power.  The  following 
outline  will  show  the  principles  of  the  process. 

Water-Gas.  —  Steam  from  a  boiler  is  carried  into  a 
furnace,  and  heated  to  a  high  temperature.  This  "  super- 
heated steam  "  is  driven  into  a  retort  containing  some  red- 
hot  anthracite  coal.  Here  a  chemical  reaction  occurs. 

C        +    H2O    =  CO  +          H 

Carbon  -f   Steam  =   Carbon  monoxide   -f  Hydrogen. 

This  mixture  of  carbon  monoxide  and  hydrogen  is  called 
WATER-GAS. 

Decomposition  of  the  Petroleum.  —  The  water-gas 
passes  over  into  another  retort  kept  intensely  hot,  into  which 
petroleum  is  introduced.  This  liquid  is  at  once  vaporized 
and  decomposed.  Its  heavy  hydrocarbons  QjHgo,  C8H18, 


CHEMISTEY.  199 

etc.,  are  broken  into  light  hydrocarbons,  such  as  marsh-gas, 
olefiant-gas,  and  other  permanent  gases. 

The  Illuminating1  Gas.  —  These  hydrocarbons,  mixed 
with  carbon  monoxide  and  hydrogen,  constitute  the  illumi- 
nating gas.  Several  of  the  hydrocarbons  are  rich  in  carbon, 
and  would  burn  with  a  smoky  flame  if  they  were  alone  ;  but 
they  are  diluted  with  the  marsh-gas,  carbon  oxide,  and  hy- 
drogen, until  they  are  able  to  burn  with  a  clean  and  brilliant 
light.  Because  the  marsh-gas,  carbon  oxide,  and  hydrogen 
are  useful  to  dilute  the  heavy  hydrocarbons,  these  constitu- 
ents are  called  the  DILUENTS,  while  the  light-giving  gases 
are  called  the  LUMINANTS. 

214.  Coal-Tar.  —  The    coal-tar   of    the    gas-works   is   a 
very  complex  substance.     When  distilled,  vapors  containing 
ammonia  first  pass  over,  and  then  a  light  oil,  known  as  coal 
naphtha,  followed  by  a  heavier  one  called  dead  oi7,  contain- 
ing a  small  portion  of  paraffine.     A  black  pitch  or  asphalt 
is  left. 

But  these  are  only  proximate  constituents  of  the  tar :  each 
is  itself  made  up  of  many  simpler  ones.  The  naphtha,  for 
example,  is  made  up  of  several  distinct  kinds  of  oil  which 
may  be  separated  by  careful  distillation,  each  having  its  own 
peculiar  boiling-point. 

215.  Carbolic  Acid.  —  One  of  the  most  important  sub- 
stances obtained  from  coal-tar  is   carbolic   acid   or  phenol 
(C6  H6  0) .     It  is  not  a  direct  product  of  distillation  ;  but  it  is 
obtained  from  the  naphtha  which  comes  over  between  300° 
and  400°  F.,  by  the  action  of  sodium  hydrate  (caustic  soda). 
When  pure,  it  is  a  white  solid,  soluble  in  alkalies,  with  a 
smell   like   creosote.      Its   most   important   property   is   its 
power  to  interrupt  decay :  it  is  a  good  disinfectant,  and  is 
in  much  demand  for  this  purpose.     It  is  used  to  some  ex- 
tent in  medicine,  and  quite  largely  in  the  manufacture  of 
colors  for  dyeing  silk  and  woolen  goods. 

216.  Benzol.  —  Benzol  (C6  H6)  is  another  important  con- 


200  CHEMISTRY. 

stituent  of  coal-tar.  It  is  a  colorless  liquid,  very  volatile 
and  very  combustible.  It  is  a  powerful  solvent  of  oils  and 
other  fatty  substances,  and  may  be  used  to  remove  grease 
spots  from  silk  or  woolen  fabrics. 

217.  Nitro- Benzol.  —  By    mixing    benzol    with    strong 
nitric  acid  a  reaction  is  brought  about,  shown  in  the  equa- 
tion, 

C6H6  +  HN03  =  C6H5N02  +  H2O. 

It  will  be  noticed  that  one  atom  of  hydrogen  in  the  benzol 
is  replaced  by  one  molecule  of  the  radical  N  O2,  forming 
C6  H5  N  (X.  This  new  substance  is  called  NITRO-BENZOL. 

Nitro-benzol  is  a  fluid  having  the  odor  of  bitter  almonds. 
It  is  used  to  some  extent  in  making  perfumes,  but  its  most 
important  use  is  in  the  production  of  aniline. 

218.  Aniline.  —  Nitro-benzol  may  be  changed  to  aniline 
in  different  ways.     Hofm aim's    method    consists    in    acting 
upon  it  by  hydrogen  set  free  from  sulphuric  acid  by  zinc. 
The  following  reaction  takes  place  :  — 

C6H5NO2  +  6H  =  C6H7N  +  2H2O. 

Losing  two  combining  weights  of  oxygen,  and  gaining  two 
of  hydrogen,  the  nitro-benzol  is  changed  to  C6H7N.  This 
new  substance  is  aniline. 

manufacture.  —  On  a  large  scale  aniline  is  made  by  a 
more  economical  method  (Bechamps'),  in  which  the  change 
is  effected  by  iron  and  acetic  acid.  One  hundred  parts  of 
the  crude  nitro-benzol  is  mixed  with  nearly  its  own  weight 
of  strong  acetic  acid  ;  and  to  this  is  added,  little  by  little, 
about  one  hundred  and  fifty  parts  of  iron-turnings.  A  com- 
plicated reaction  takes  place  ;  and  when  the  mixture  is  after- 
ward heated,  impure  aniline  is  obtained.  It  is  purified  by 
treating  it  with  lime  or  soda,  and  re-distilling  it.  By  this 
means  the  crude  aniline  of  commerce  is  obtained. 

Properties.  —  Aniline,  when  pure,  is  a  colorless  liquid, 
heavier  than  water,  soluble  in  alcohol  and  ether,  and  very 


CHEMISTRY.  201 

slightly  in  water.  Its  most  remarkable  property  is  that  ot 
acquiring  various  and  rich  colors  by  the  action  of  different 
oxidizing  agents. 

Aniline  Ked.  — If,  for  example,  aniline  is  heated  with 
arsenic  acid  to  about  150°  C.,  a  part  of  its  hydrogen  will  be 
extracted  as  water,  and  there  will  remain  what  is  called 
HOSANILINE,  in  combination  with  the  arsenic.  Sodium 
hydrate  may  then  be  added  :  it  will  remove  the  arsenic,  and 
precipitate  the  rosaniline. 

Let  this  rosaniline  be  treated  with  hydrochloric  acid,  and  a 
rosaniline  chloride  will  be  formed.  This  salt  is  the  so-called 
ANILINE  RED.  It  occurs  in  crystals,  having  a  green  luster, 
but  its  solution  in  water  or  in  alcohol  is  a  beautiful  red. 

Aniline  Dyes.  —  By  the  action  of  other  chemicals  on 
aniline  or  its  salts,  many  coloring  matters  are  obtained. 
Various  rich  shades  of  red,  yellow,  green,  blue,  and  black, 
indeed,  almost  every  variety  of  tint,  are  made,  and  largely 
used  in  the  arts. 

219.  Slow  Destructive  Distillation.  —  The  decay  of 
vegetable  matter,  when  buried  in  the  moist  earth,  or  covered 
by  the  water  and  mud  of  bogs  and  marshes,  is  somewhat 
different  from  its  decay  when  exposed  to  the  air.  Instead 
of  giving  off  carbon  dioxide  and  water,  and  crumbling  to  a 
black  mold,  it  gives  off  marsh-gas  and  other  hydrocarbons, 
and  yields  a  residue  of  coal. 

The  chief  constituents  of  wood  are  carbon,  hydrogen,  and 
oxygen ;  the  first  two  being  far  the  most  abundant.  On 
exposure  to  air,  oxygen  from  the  atmosphere  combines  with 
hydrogen  and  carbon  of  the  wood  to  form  water  and  carbon 
dioxide,  leaving  oxygen  in  combination  with  what  remains  of 
both  these  elements,  forming  humus  ;  but  when  the  air  is 
excluded,  the  process  of  decay  must  consist  chiefly  in  the 
re-arranging  of  the  elements  of  the  wood  itself.  Its  oxygen 
takes  carbon  enough  to  form  carbon  dioxide  ;  its  hydrogen 
takes  carbon  also,  and  forms  gaseous  or  liquid  compounds ; 


202  CHEMISTRY. 

while  the  excess  of  carbon,  not  thus  used,  is  left  in  the  form 
of  coal. 

Varieties  of  Coal.  —  Vast  quantities  of  vegetable  mat- 
ter, accumulating  in  low  wet  lands  of  warm  countries, 
gradually  beeome  covered  with  water ;  and  sometimes,  by 
the  sinking  of  the  land,  they  are  buried  under  mud  and  sand 
brought  over  them  by  streams  or  floods.  Thus  shut  off  from 
the  air,  a  slow  decay  goes  on,  by  which  they  are  at  last 
changed  to  coal.  The  different  varieties  of  coal  mark  the 
different  stages  of  the  process.  In  peat  the  change  is  only 
well  begun :  in  anthracite  coal  the  process  is  at  an  end. 
The  warmth  of  the  earth  assists  the  change  ;  and  the  great 
pressure  of  the  material,  accumulating  for  ages  upon  it, 
must  have  had  much  to  do  with  'the  final  compactness  of  the 
remaining  coal.  In  bituminous  coal  the  liquid  hydrocarbons 
remain,  but  may  be  driven  away  by  heat :  from  anthracite 
they  have  already  escaped. 

Origin  of  Petroleum.  —  Numerous  and  extensive  beds 
of  coal  have  thus  been  produced  by  the  slow  distillation  of 
vegetable  matter  during  past  ages  of  the  earth's  history. 

But  what  has  become  of  the  liquid  hydrocarbons  which 
must  have  been  formed,  but  which  are  no  longer  held  in  the 
hard  coal  ?  Moreover,  during  the  deposition  of  other  rocks 
in  which  no  coal  is  found,  there  is  abundant  evidence  that 
plants  were  growing,  and  they,  too,  must  have  been  decom- 
posed in  a  similar  way  :  what  has  become  of  the  products  of 
their  decay  ? 

The  gaseous  products  would,  of  course,  for  the  most  part, 
escape  into  the  air ;  and  it  would  be  natural  to  suppose  that 
the  liquid  products  would  gradually  collect  in  cavities  and 
fissures  in  the  rocks.  Now,  inflammable,  oily  substances, 
issuing  often  in  large  quantities  from  the  fissures  of  rocks, 
have  been  long  known.  To  them  the  general  name  of  petro- 
leum has  been  given.  They  resemble  the  liquid  products 
obtained  by  destructive  distillation  of  wood ;  and  it  is 
believed  that  they  are  the  products  of  the  slow  decom- 


CHEMISTRY.  203 

position  of  organic  matter,  chiefly  vegetable.  Petroleum, 
or  rock-oil,  is,  then,  the  liquid  hydrocarbon  substances  given 
off  in  the  slow  process  of  the  decay  of  vegetable  matter  long 
buried  in  the  earth. 


SECTION  VII. 

THE  SUGARS. 

220.  Sugar.  —  The  term  "  sugar,"  when  used  in  chem- 
istry, is  not  the  name  of  any  single  substance,  but  the 
name  of  a  class.  The  sugars  are,  all  of  them,  compounds 
of  carbon,  hydrogen,  and  oxygen  ;  and  in  their  composition 
there  is  this  peculiarity,  viz.,  TJie  hydrogen  and  oxygen  are 
in  the  proportions  to  form  tuater.  There  are  many  varieties 
of  sugars  ;  but  they  may  be  grouped  in  three  classes,  —  the 
sucroses,  the  glucoses,  and  the  amyloses. 

The  Sucroses.  —  Cane-sugar,  so  common  and  well 
known,  and  milk-sugar,  or  lactose,  obtained  by  evaporating 
the  whey  of  fresh  milk,  are  members  of  the  first  class. 
Cane-sugar  occurs  in  the  juices  of  many  plants.  It  is 
obtained  by  evaporating  the  sap  of  the  sugar-maple,  or  the 
juice  of  the  beet,  and  in  far  larger  quantities  from  the  juice 
of  the  sugar-cane.  Its  general  character  is  well  known.  Its 
composition  is  represented  by  the  formula  C12  H22  On.  When 
strongly  heated,  it  yields  water  and  a  dark-colored  residue 
called  caramel.  One  of  its  most  curious  properties  is  shown 
in  its  action  upon  polarized  light :  it  turns  the  plane  of 
polarization  to  the  right  hand. 

The  Glucoses.  —  Grape-sugar  and  fruit-sugar  are  glu- 
coses. They  are  found  together  in  many  kinds  of  fruit, 
especially  in  the  grape.  They  have  the  same  composition, 
C6  H12  O6,  and  yet  differ  in  several  properties.  Grape-sugar 
easily  crystallizes :  fruit-sugar  never  does.  The  latter  is 
more  soluble,  and  rotates  the  plane  of  polarization  to  the  left, 
the  former  to  the  right. 


204  CHEMISTRY. 

Sucrose  Changed  to  Glucose.  —  When  cane-sugar  is 
acted  on  by  dilute  sulphuric  acid,  a  reaction  takes  place  by 
which  the  cane-sugar  is  changed  into  grape-sugar  and  fruit- 
sugar,  by  taking  the  elements  of  a  molecule  of  water :  — 

CaHaOu    +    H20    =      C6H1206      +     C6H1206, 
Cane-sugar  +  Water  =  Grape-sugar  -f  Fruit-sugar. 

The  Amyloses.  —  Starch  is  the  most  familar  example  of 
the  amyloses.  It  consists  of  a  white  powder,  composed  of 
granules,  which  have  different  size  and  shape  in  different 
varieties :  those  of  potato-starch  being  about  .007  inches  in 
diameter;  of  beet- root,  about  .0002  inches.  These  granules 
are  not  soluble  in  cold  water,  but  when  heated  in  water 
they  swell  and  split  open  ;  and,  if  the  paste  thus  formed  is 
boiled  in  a  larger  quantity,  the  starch  is  at  last  dissolved. 

When  free  iodine  is  brought  in  contact  with  starch,  a  com- 
pound, having  a  rich  blue  color,  is  made.  This  action  is  the 
most  delicate  test  for  the  presence  of  starch.  To  show  its 
presence  in  a  potato,  for  example,  let  the  freshly  cut  surface 
of  the  vegetable  be  washed  with  a  solution  of  iodine. 

The  composition  of  starch  is  shown  by  its  formula, 
C6  H10  O5.  By  the  action  of  dilute  sulphuric  acid,  starch  is 
changed  into  dextrine  and  grape-sugar. 

Dextrine.  —  Dextrine,  or,  as  it  is  more  commonly  called, 
British  gum,  is  another  amylose.  It  is  very  soluble  in  water, 
and  it  is  used  sometimes  instead  of  gum-arabic  in  calico- 
printing  and  other  arts.  It  is  made  from  starch,  not  only  by 
means  of  dilute  sulphuric  acid,  but  by  simply  heating  the 
starch  to  about  150°  C.  (302°  F.),  or  by  the  action  of 
diastase  (a  substance  contained  in  malt) .  By  the  continued 
action  of  the  diastase  the  starch  is  first  changed  into  dextrine 
and  grape-sugar,  and  the  dextrine  is  finally  changed  also  into 
grape-sugar. 

3(C6H10O5)   +     H2O     =  2(C6H10O5)    +     C6H12O6, 
Starch       -f-    Water    =     Dextrine      +  Grape-sugar. 


CHEMISTRY.  205 

Dextrine  and  starch  have  the  same  composition,  C6H10O5, 
but  their  properties  are  different.  Dextrine  is  soluble  in 
water,  and  is  reddened,  instead  of  being  turned  blue,  by 
iodine.  Bodies  having  the  same  composition,  but  different 
properties,  are  said  to  be  isomeric.  Dextrine  and  starch  are 
isomeric  substances. 

221.  Ferment.  —  By  the  term  ferment  we  mean  an 
organic  compound  containing  nitrogen,  and  which  readily 
decomposes  on  exposure  to  air.  Any  substance  containing 
nitrogen,  and  partially  decomposed,  will  act  as  a  ferment. 
Yeast  is  the  most  familar  example.  When  the  sweet  juices 
of  vegetables  are  exposed  to  the  air,  a  ferment  is  soon 
formed  in  them  ;  and,  the  smallest  quantity  of  ferment  being 
present,  an  action  is  started  by  it  which  goes  on  until  the 
entire  body  of  liquid  is  decomposed. 

Fermentation.  —  The  decomposition  caused  by  ferments 
is  called  FERMENTATION.  It  may  be  easily  illustrated  by 
experiment.  Dissolve  about  one  hundred  grains  of  honey, 
or  it  may  be  molasses,  in  a  pint  of  water ;  fill  a  small  flask 
with  the  solution,  and  add  a  few  drops  of  brewer's  yeast. 
Close  the  neck  of  the  flask  with  the  hand,  and  invert  it  in  a 
dish  holding  some  of  the  same  sirup,  and  leave  it  in  a  warm 
place  for  twenty-four  hours.  Fermentation  soon  begins  ;  a 
colorless  gas  collects  in  the  flask,  which,  by  lime-water,  may 
be  shown  to  be  carbon  dioxide,  while  alcohol  remains  in  the 
fluid.  Thus :  — 

CeH^Oe     =     2C2H60     +  2  C O2, 

Sugar       =      Alcohol      -f-  Carbon  dioxide. 

All  fermentation  which  produces  chiefly  alcohol  and  carbon 
dioxide  is  called  the  ALCOHOLIC  or  VINOUS  fermentation. 
The  process  goes  on  best  at  a  temperature  of  25°  or  30°  C. 

Spirituous  Liquors.  —  The  spirituous  liquors  of  com- 
merce, such  as  brandy,  gin,  and  whiskey,  are  produced  by 
distilling  fermented  liquids.  The  fermented  liquid  obtained 


206  CHEMISTRY. 

from  malted  grain  is  called  BEER  ;  that  from  the  juice  of  the 
grape  is  called  WINE.  By  distilling  these,  and  adding  various 
substances  to  color  and  flavor  the  result,  different  kinds  of 
liquor  are  made.  Brandy  is  made  by  distilling  wine  ;  gin  is 
made  from  different  kinds  of  corn  spirits,  its  flavor  being 
given  by  juniper-berries,  sweet-flag,  licorice-powder,  and 
several  other  substances.  Whisky  is  also  obtained  by  distill- 
ing the  fermented  liquor  from  corn. 

The  intoxicating  principle  in  all  these  liquors  is  alcohol, 
which  has  been  produced  by  fermentation. 

222.  The  Acetous  Fermentation.  —  An  alcoholic 
liquid,  which  contains  a  small  quantity  of  a  ferment,  and 
is  in  the  presence  of  air,  yields  acetic  acid.  Acetic  acid  is 
the  acid  which  gives  sourness  to  vinegar. 

Fermentation  in  which  acetic  acid  is  the  chief  product  is 
called  the  ACETOUS  FERMENTATION. 

Production  of  Vinegar.  —  When  an  alcoholic  liquid  is 
exposed  to  the  air  in  a  warm  place,  a  little  yeast  or  other 
nitrogenous  matter  in  it  will  start  an  action  by  which  the 
alcohol  is  changed  into  vinegar.  ; '  A  good  extemporaneous 
vinegar  may  be  prepared  by  dissolving  one  part  of  sugar  in 
six  of  water,  with  one  part  of  brandy,  and  a  little  yeast. 
The  mixture  is  put  into  a  cask,  with  the  bung-hole  open,  and 
kept  at  a  temperature  between  70°  and  80°  F.  In  from  four 
to  six  weeks  the  clear  vinegar  may  be  drawn  off."  (Brande 
&  Taylor.)  A  still  more  simple  process  consists  in  soaking 
crushed  apple-skins  in  soft  water  for  a  few  days,  straining 
the  juice,  and  letting  it  stand  exposed  to  the  air  in  a  warm 
place  for  several  days  :  an  excellent  vinegar  is  the  result. 

Acetic  Acid.  —  Common  vinegar  is  a  very  dilute  acetic 
acid.  Its  quality  depends  upon  the  proportion  of  acid  it 
contains,  and  the  absence  of  other  impurities.  The  compo- 
sition of  acetic  acid  is  shown  by  the  symbol  C2  H4  O2.  It  is 
a  colorless  liquid,  with  a  powerful  and  peculiar  odor,  which, 
once  experienced,  is  afterward  easily  recognized. 


CHEMISTRY.  207 

Fermentation  of  Alcohol.  —  The  chemical  action  by 
which  alcohol  is  changed  to  acetic  acid  is  called  the  acetous 
fermentation.  And  yet  it  is  not  in  all  respects  a  true  fer- 
mentation. It  is  not  a  decomposition,  but  rather  an  oxida- 
tion, as  may  be  seen  by  comparing  the  symbols  of  alcohol 
and  acetic  acid.  In  this  respect  the  action  is  a  case  of  com- 
bustion rather  than  of  fermentation.  It  can  take  place  only 
in  the  presence  of  air,  so  that  the  action  is  not  entirely  due 
to  a  ferment.  Yet,  on  the  other  hand,  it  will  not  occur, 
except  in  presence  of  a  nitrogenous  substance,  to  which  the 
term  ferment  has  been  given  ;  and  hence  the  reaction  is  very 
naturally  called  a  fermentation. 

REVIEW. 

I.— SUMMARY   OF  PRINCIPLES. 

223.  Organic  chemistry  is  the  chemistry  of  the  compounds 
of  carbon. 

The  compounds  of  carbon  are  the  products  of  the  decom- 
position of  organic  bodies  :  with  some  exceptions,  we  have 
no  evidence  that  they  exist  ready  formed  in  the  living  plant 
or  animal. 

A  large  number  of  these  substances  contain  only  carbon 
and  hydrogen  ;  others  contain  oxygen  in  addition ;  and  n 
few  contain  other  elements,  especially  nitrogen. 

Marsh-gas  is  the  simplest  hydrocarbon.  Its  molecule  is 
represented  by  C  H4. 

It  is  found  in  nature  ready  formed.  In  many  places  it 
issues  in  large  quantities  from  the  earth :  it  collects  in  mines, 
and  it  also  issues  from  the  mud  of  stagnant  pools. 

A  homologous  series  is  a  series  of  compounds  containing 
the  same  elements,  in  which  there  is  a  common  difference  in 
the  molecules  of  successive  members. 

Marsh-gas  is  the  first  member  of  a  homologous  series  of 
hydrocarbons,  in  which  the  common  difference  is  C  H2. 


208  CHEMISTRY. 

The  densities  of  these  hydrocarbons  increase  regularly  as 
the  molecules  become  more  complex. 

Carbon  is  quadrivalent,  and  its  atoms  are  able  to  combine 
with  one  another :  these  two  assumptions  furnish  an  explana- 
tion of  the  paraffine  series. 

Petroleum  contains  several  members  of  this  series  from 
C4H10  to  CgHao,  inclusive,  beside  several  hydrocarbons 
belonging  to  other  series. 

The  boiling-points  of  these  hydrocarbons  differ:  hence 
they  may  be  separated  by  fractional  distillation.  Several 
commercial  products  are  obtained  by  the  fractional  distillation 
of  petroleum. 

Common  alcohol  is  obtained  by  distilling  a  fermented  liquid. 
It  is  a  colorless  liquid,  lighter  than  water,  very  volatile  and 
combustible. 

The  molecule  of  alcohol  is  C2H6O.  Its  rational  formula 
isC2H5HO.  According  to  this  formula  its  chemical  name 
should  be  ethyl  hydrate. 

It  may  be  regarded  as  derived  from  ethane,  C2  H6,  by  the 
substitution  of  H  O  for  one  atom  of  H. 

Common  alcohol  is  one  of  a  large  number  of  analogous 
substances  which  constitute  a  series  of  alcohols. 

An  alcohol  is  a  compound  derived  from  a  hydrocarbon 
by  substituting  a  molecule  of  hydroxyl  for  an  atom  of 
hydrogen. 

A  radical  is  a  group  of  atoms  which  passes  bodily  from 
one  combination  to  another  in  chemical  actions.  The  hydro- 
carbon combined  with  hydroxyl  in  an  alcohol  is  called  an 
alcohol  radical. 

Ether  is  a  limpid  liquid,  very  volatile,  very  combustible, 
a  powerful  solvent,  and  an  anaesthetic. 

It  is  obtained  by  treating  ethyl  or  common  alcohol,  with 
sulphuric  acid.  Its  composition  is  represented  by  C4H10O, 
or  by  the  rational  formula  (C2H5)2O.  According  to  this 
formula  its  chemical  name  should  be  di-ethyl  oxide. 

Common  ether  is  one  member  of  a  large  class  of   sub- 


>*  0»  TH1        ^^ 

CHEMISTRY.  209 


stances  called  the  ethers.  An  ether  is  a  substance  produced 
by  the  action  of  a  strong  acid  on  an  alcohol.^ 

The  composition  of  methyl  ether  is  represented  by  C2  H6  O, 
or  by  its  rational  formula  (CH3)2O. 

But  the  composition  of  common  alcohol  is  also  represented 
by  the  same  formula,  C2H6O.  Hence  these  two  substances 
furnish  an  example  of  isomerism,  —  having  the  same 
chemical  composition,  but  different  properties. 

Isomerism  is  explained  by  supposing  the  atoms  of  the 
substances  to  be  differently  arranged  in  the  molecules. 

The  rational  formula  may  show  the  different  groupings  of 
the  atoms  which  we  suppose  to  exist.  Thus  we  write  for 
alcohol  C2H5OH,  and  for  methyl  ether  (CH3)2O. 

The  graphic  form  of  the  rational  formulas  shows  this 
difference  still  more  clearly.  Thus  :  — 

H     H  H  H 

II  II 

H— C— C— O— H,  H— C— O— C— H, 

II  II 

H     H  H  H 

Alcohol.  Methyl  ether. 

In  the  first  we  discover  two  groups,  C2H5  and  OH.  In 
the  second  we  discover  two  groups,  CH3  and  C  H3,  bound 
together  by  oxygen. 

Isomeric  substances  are  very  numerous  among  the  com- 
pounds of  carbon. 

Olefiant  gas  is  a  colorless  gas,  very  combustible  and 
explosive.  It  is  represented  by  C2H4. 

This  gas  is  the  first  member  of  a  homologous  series,  —  the 
olefines. 

Destructive  distillation  is  the  decomposition  of  an  organic 
substance  by  heat  in  the  absence  of  air.  The  products  are 
solid,  liquid,  and  gaseous. 

Illuminating  gas  is  made  by  the  destructive  distillation  of 
soft  coal,  sometimes  of  other  materials. 


210  CHEMISTRY. 

The  solid  residue  is  coke.  The  liquid  products  are  col- 
lectively called  coal-tar  and  ammoniacal  water.  The  gaseous 
product  contains  the  luminants,  the  diluents,  and  the  im- 
purities. 

Carbolic  acid  and  benzol  are  among  the  valuable  products 
obtained  directly  from  coal-tar.  From  benzol  comes  nitro- 
benzol,  and  finally  aniline.  From  aniline  many  rich  and 
valuable  dyes  are  made. 

Organic  matter  buried  in  the  earth  undergoes  a  slow  pro- 
cess of  destructive  distillation.  The  varieties  of  mineral 
coal,  and  petroleum  or  rock-oil,  are  doubtless  the  products  of 
such  a  process. 

Sugar  is  a  compound  of  carbon,  hydrogen,  and  oxygen, 
in  which  the  last  two  are  in  the  proportions  to  form 
water. 

There  are  three  classes,  —  the  sucroses,  the  glucoses,  and 
the  amy loses. 

The  sucroses  may  be  changed  to  glucose  by  dilute  sulphuric 
acid.  The  same  is  true  of  the  amyloses. 

Fermentation  is  a  decomposition  caused  by  ferments.  The 
vinous  fermentation  consists  in  the  change  of  glucose  into 
carbon  dioxide  and  alcohol. 


II.  —  EXERCISES. 

Define  organic  chemistry.  What  is  an  organized  body? 
What  are  organic  substances?  With  which  of  these  does 
chemistry  deal? 

Define  hydrocarbon.  Name  the  simplest  hydrocarbon,  and 
give  its  formula.  Where  is  marsh-gas  found  in  nature? 
What  are  its  properties  ?  How  may  we  prove  that  its  mole- 
cule contains  four  atoms  of  hydrogen  ? 

By  what  other  names  is  marsh-gas  known  ?  What  does 
the  name  methyl  hydride  signify?  How  would  its  formula 
be  written  ? 

Give  the  formulas  and  names  of  the  first  four  members  of 


CHEMISTRY.  211 

the  marsh-gas  series.  How  do  chemists  explain  the  fact 
that  hydrogen  and  carbon  can  form  so  many  compounds? 
Write  the  graphic  formulas  for  the  first  four  members  of  the 
series. 

What  are  the  properties  of  this  series  ? 

What  ie  petroleum?  What  is  its  composition?  Define 
fractional  distillation.  What  is  kerosene?  Benzine? 
Naphtha  ? 

How  may  alcohol  be  obtained  ?  What  is  absolute  alcohol  ? 
How  may  it  be  obtained?  What  are  the  properties  of 
alcohol  ? 

What  is  the  composition  of  alcohol  ?  If  we  call  it  ethyl 
hydrate,  how  should  we  write  its  formula?  What  evidence 
is  given  that  the  molecule  does  contain  these  two  groups  ? 

By  what  substitution  may  alcohol  be  derived  from  ethane? 

Define  the  term  alcohol.     How  are  the  alcohols  named? 

Define  the  term  radical.  Show  that  C  H3  remains  unbroken 
while  methane  is  passing  through  the  changes  to  become 
methyl  alcohol. 

What  is  ether?  What  is  its  effect  when  breathed?  What 
is  the  effect  of  its  evaporation?  What  are  some  of  its 
uses? 

How  is  ether  prepared  ?     Give  the  chemical  change. 

To  what  class  of  substances  is  the  name  ether  given? 
Which  of  these  is  the  common  ether  ?  What  is  its  formula  ? 

What  is  olefiant  gas  ?  What  are  some  of  its  properties  ? 
What  are  its  other  names  ? 

What  are  the  olefmes?  From  what  sources  may  these 
bodies  be  derived  ? 

Define  homologous  series. 

What  is  destructive  distillation? 

Describe  the  experiment  showing  the  destructive  distilla- 
tion of  wood. 

What  is  said  of  pyroligneous  acid? 

What  is  said  of  wood- tar  ? 

What  is  said  of  methyl  alcohol  ? 


212  CHEMISTRY. 

What  is  said  of  creosote  ?  What  is  its  most  curious  and 
valuable  property? 

How  may  paraffine  be  obtained?  What  are  some  of  its 
properties  ? 

What  is  said  of  other  products  of  destructive  distillation  ? 
Do  these  substances  exist  in  the  plant  ? 

Give  a  brief  description  of  the  manufacture  of  illuminating 
gas? 

What  is  said  of  mineral  coal?  What  are  two  principal 
varieties?  Which  is  used  in  making  the  gas? 

Describe  the  heating  in  iron  retorts. 

What  substances  are  driven  off? 

What  becomes  of  this  mixture?  What  occurs  in  the 
hydraulic  main  ? 

Describe  the  next  step  in  the  process. 

What  impurities  still  remain  ?     How  are  they  removed  ? 

Into  what  is  the  purified  gas  finally  conducted  ?  Describe 
the  gasometer,  and  explain  its  action. 

From  what  other  substance  is  illuminating  gas  made? 
What  is  water-gas  ?  How  is  it  made  ?  How  are  water-gas 
and  petroleum  converted  into  illuminating  gas  ? 

Of  what  does  the  illuminating  gas  consist  ? 

What  is  the  formula  of  carbolic  acid  ?  How  is  this  acid 
obtained?  What  are  some  of  its  properties?  Its  uses? 

What  is  the  formula  of  benzol?  What  are  some  of  its 
properties  ? 

Give  the  reaction  by  which  nitro- benzol  is  formed  ?  What 
are  its  uses  ? 

Show  how  nitro-benzol  may  be  changed  to  aniline. 
Describe  the  method  adopted  in  the  arts.  What  are  the 
properties  of  aniline? 

How  is  aniline  changed  into  aniline  red?  How  are  other 
aniline  dyes  made  ? 

How  have  mineral  coal  and  petroleum  been  formed  ? 

Describe  the  decay  of  vegetable  matter  when  kept  from 
the  air.  Show  wherein  this  decay  differs  from  decay  in  air. 


CHEMISTRY.  213 

Explain  the  formation  of  the  varieties  of  coal. 

In  the  formation  of  mineral  coal,  would  these  gases  and 
volatile  liquids  be  driven  off  ?  What  would  naturally  become 
of  them  ?  Is  any  thing  of  the  kind  now  to  be  found  in  the 
rocks  ?  What  name  is  given  to  them  ?  Describe  them. 

Define  the  term  sugar.     Name  the  three  classes. 

Name  varieties  of  sucrose.  How  is  cane-sugar  obtained? 
What  is  its  composition  ?  What  are  its  properties  ? 

Name  varieties  of  glucose.  What  is  their  composition? 
Wherein  do  they  differ  ?  Give  the  reaction  by  which  cane- 
sugar  is  changed  into  grape  and  fruit  sugar. 

What  are  the  properties  of  starch  ?  The  test  for  its  pres- 
ence? Its  composition? 

What  is  dextrine  ?  How  is  it  made  from  starch  ?  Give 
the  symbols,  and  explain  the  reaction. 

What  is  a  ferment?     Name  a  familiar  example. 

What  is  fermentation?  Describe  the  experiment,  and 
explain  the  reaction.  What  is  the  alcoholic  fermentation? 

How  are  spirituous  liquors  obtained?  Name  some  com- 
mon kinds,  and  tell  how  they  are  made. 

What  is  the  intoxicating  principle  in  all  kinds  ? 

How  may  alcohol  be  changed  to  acetic  acid  ? 

Give  the  formula  for  acetic  acid. 

Describe  the  acid. 

What  is  common  vinegar  composed  of?  What  is  the 
acetous  fermentation?  Is  it  in  all  respects  a  true  fermenta- 
tion? 


214  CHEMISTRY. 


CHAPTER  IV. 
THE  METALS. 


SECTION    I. 
GENERAL  DESCRIPTION. 

224.  Characteristic  Properties.  —  The  peculiarities  of 
metallic  elements  are  more  or  less  familiar.  Their  luster,  as 
of  silver ;  their  malleability,  as  of  gold  and  zinc ;  their  duc- 
tility, as  of  iron  and  copper ;  together  with  their  power  to 
conduct  heat  and  electricity,  —  are  their  most  characteristic 
properties.  One  or  more  of  these  properties  are  possessed 
by  some  non-metals  ;  and,  on  the  other  hand,  some  metals 
have  them  only  in  a  slight  degree.  Indeed,  nature  seems  to 
have  drawn  no  precise  line  of  division  between  the  two  classes. 
Certain  elements,  arsenic  and  antimony  for  example,  have 
been  classed  with  metals,  but  are  considered  now  to  be  non- 
metals  ;  while  even  hydrogen,  because  of  its  chemical  rela- 
tions, is  thought  by  some  to  be  a  metal. 

Melting-Points.  —  The  metals,  with  the  exception  of 
mercury,  are  solids  at  ordinary  temperature.  Some  are 
easily  melted,  as  potassium,  at  62°  5  C.  (144°  5  F.)  ;  others 
melt  with  difficulty,  as  iron  at  1,600°  C.  (2,912°  F.)  ;  while 
others,  like  platinum,  melt  only  in  the  intense  heat  of  the 
oxy hydrogen  blow-pipe. 

Density.  —  Osmium  is  the  heaviest  of  metals,  22.47  times 
heavier  than  water ;  others,  as  potassium  and  sodium,  are 
so  light  that  they  will  float  on  the  surface  of  water.  Lithium 
is  the  lightest  of  all :  its  specific  gravity  is  only  .594. 


CHEMISTRY. 


215 


Condition  in  Nature.  —  A  few  metals,  copper  and  gold 
for  example,  are  found  in  nature  in  the  metallic  state :  this 
condition  is  commonly  called  NATIVE.  But  in  the  native 
state  they  are  seldom  pure :  two  or  more  are  combined. 
Combinations  of  metals  are  called  ALLOYS.  The  metals  are, 
however,  usually  found  combined  with  non-metals  ;  and  such 
compounds  are  called  ORES. 

225.  Classification  of  the  Metals In   the  following 

table  the  metals  are  classed  so  as  to  bring  together  those 
which  most  closely  resemble  each  other.  Many  of  the  metals 
are  rare,  and  not  important  to  the  general  student :  others 
are  of  the  greatest  use  and  interest.  Of  these  last  the 
names  are  printed  in  capitals,  and  to  the  description  of  them 
we  are  to  pay  the  more  particular  attention. 


1.  —Metals  of  the  Alkalies. 

5.  —  Zinc  Class. 

POTASSIUM  .    . 

.    K.1 

ZINC    

Zn.« 

SODIUM    .    .    . 

.    Na.' 

Magnesium  .     .     . 

Mg." 

Lithium  .     .     . 

.    Li.' 

Cadmium      .     .     . 

Cd.11 

Caesium    .     .     . 

.     Cs.1 

Beryllium     .     .     . 

Be. 

Rubidium     .     . 

.     Rb.1 

6.  —  Iron  Class. 

2.—  Metals    of    the 

Alkaline 

IRON        .... 

Fe.n«  IV 

Earths. 

Manganese    .     .     . 

Mn."«IV 

CALCIUM  .    .    . 

.     Ca.11 

Nickel 

Ni.11'  1V 

Strontium     .     . 

.     Sr." 

Cobalt  . 

Co.u»IV 

Barium    .     .    . 

.     Ba.11 

3.  —  The  Aluminium 

Class. 

7.  —  Tin  Class. 

ALUMINIUM  .     . 

.    A1.»'IV 

TIN      .... 

Sn.11*  rv 

Indium    .     .     . 

.     In. 

Titanum  .... 

Ti  H.IV 

Gallium  .     .    . 

.     Ga. 

Zirconium     .     .     . 

Zr. 

Thorium  .    „     ... 

Th. 

4.  —  Cerium  Class. 

Cerium    .     .     . 

.     Ce. 

8.  —  Chromium  Class.. 

Ytrium     .     .     . 

.     Y. 

Chromium    .     .     . 

Cr.n.  iv 

Erbium    .     .     . 

.     Er. 

Molybdenum     .     . 

Mo. 

Lanthanum  .     . 

.     La. 

Tungsten      .     .     . 

W. 

Didymium    .     . 

.     Di. 

Uranium.     .     .     . 

U. 

216 


CHEMISTRY. 


9.  —  Antimony  Class. 
ANTIMONY   .    .    . 
ARSENIC  .... 
BISMUTH  .... 

Sb.'» 
As."1 
Bi."1 

11.  —  Silver  Class. 
Copper     .... 
Mercury  .... 
Silver                 .     . 

Cu.n 
Hg.« 

Ae  l 

Vanadium  .  .  . 
Niobium  .... 

T^  O  T»  +  0  1  11  TV* 

Y. 
Hb: 

Ta 

12.  —  Gold  Class.     . 
GOLD 

•"•&• 
Au.111 

1  uli  III  1  III  1  1 

10.  —  Lead  Class. 

i  ;  i  . 
Pb." 

PLATINUM    .    .    . 
Palladium     .     .     . 
Rhodium  .... 
Ruthenium  . 

Pt. 
PI. 
Rh. 
Ru. 

Thallium  .  .  . 

Th. 

Iridium    .... 
Osmium   .... 

Ir. 
Os. 

SECTION   II. 

METALS   OF   THE   ALKALIES. 

226.  General  Description.  —  The  metals  of  the  first 
class  are  very  soft  and  light,  having  so  violent  an  attraction 
for  oxygen  that  they  can  decompose  water  at  any  tempera- 
ture. They  are  univalent. 

Of  this  class  only  potassium  and  sodium  are  of  interest  to 
the  student ;  and  even  these  metals  are  of  little  use,  and  are 
important  only  because  their  compounds  are  of  great  value 
in  the  arts. 

Illustration  of  these  Class  Properties.  —  A  piece  of 
potassium  or  of  sodium  may  be  molded  in  the  fingers  like 
wax,  and  if  dropped  upon  water  it  floats. 

Upon  a  piece  of  ice,  in  a  small  cavity  made  for  the  pur- 
pose, place  a  small  fragment  of  potassium  :  a  purple  flame 
springs  up,  as  if  the  ice  had  been  set  on  fire.  A  smart  ex- 
plosion usually  ends  the  experiment ;  and  if  we  then  examine 
the  water  that  is  left  in  the  cavity  of  the  ice,  we  find  it  to 
contain  potassium  hydrate  (potash) .  So  strong  is  the  attrac- 
tion of  this  metal  for  oxygen,  that  it  decomposes  water,  even 
at  the  temperature  of  ice.  This  is  true  of  the  other  members 
of  the  group. 

The  Reaction.  —  If  we  study  the  reaction  taking  place 


CHEMISTRY.  217 

in  the  experiment,  we  shall  see  that  the  metal  is  univalent. 
Thus :  — 

H20  +  K  =  KHO  +  H. 

One  combining  weight  of  potassium  has  simply  replaced 
one  of  the  two  combining  weights  of  hydrogen  in  the  mole- 
cule of  water.  A  similar  reaction  would  occur  with  the  other 
members  of  the  group.  The  potassium  hydrate  formed  is  an 
ALKALI  ;  the  other  hydrates  of  the  group  are  also  alkalies. 
The  alkalies  differ  from  most  other  metallic  hydrates  in  their 
power  to  withstand  heat :  heat  alone  will  not  decompose  them. 

227.  Manufacture   of    Potassium    Carbonate.  —  The 

ashes  of  wood,  mixed  with  about  five  per  cent  of  lime,  are 
placed  in  tubs,  and  drenched  with  successive  portions  of  fresh 
water.  As  the  water  soaks  through  the  ashes,  it  dissolves 
out  the  soluble  constituents,  among  which  is  the  potassium 
carbonate.  This  process  is  called  leaching.  The  solution 
known  as  LYE  is  put  into  broad  and  shallow  pans,  and  evapo- 
rated. The  solid  residue  is  called  CRU£>E  POTASH.  By 
strongly  heating  this  substance,  much  of  its  impurities  may 
be  driven  off  :  the  purer  carbonate  remaining  is  called  PEARL- 
ASH. 

A  pure  salt  may  be  obtained  by  dissolving  the  pearlash, 
and  then  letting  it  crystallize.  The  salt  crystallizes  while 
the  impurities  are  still  in  solution  :  at  this  point  the  fluid  is 
drawn  off,  and  the  crystals  left.  The  symbol  of  the  pure 
substance  is  K2  C  O3. 

228.  Preparation    of    Potassium    Hydrate.  —  Potas- 
sium hydrate  (KHO)   is  obtained  by  boiling  a  solution  of 
the    carbonate  with  slaked   lime    (Ca(HO)2).     A  reaction 
occurs,  in  which  the  potassium  of  the  carbonate  is  substi- 
tuted for  the  calcium  of  the  calcium  hydrate,  or  slaked  lime, 
and   by   this   action   potassium    hydrate    is    formed,    which 
remains  in  solution,  while  the  calcium   carbonate  produced 
falls  to  the  bottom  as  a  heavy  powder. 


218  CHEMISTRY. 

The  clear  solution  is  afterward  evaporated  to  dryness,  and 
the  solid  hydrate  is  then  fused  and  run  into  molds. 

Properties.  —  Potassium  hydrate  is  very  soluble  in  water, 
and  has  a  strong  affinity  for  carbonic  acid.  It  greedily  takes 
both  these  substances  from  the  air,  until  at  length  the  entire 
mass  of  hydrate  is  changed  into  a  sirup  of  the  carbonate. 
To  indicate  this  property  of  dissolving  in  water  absorbed 
from  the  air,  the  term  DELIQUESCENCE  is  used. 

229.  Sodium    Chloride.  —  Sodium     chloride,     so    well 
known  as  common  salt   (NaCl),   is  everywhere  abundant. 
In  many  parts  of  the  world  it  occurs  in  thick  beds,   from 
which  it  may  be  mined.     Large  quantities  are  obtained  by 
evaporating    the    water    of    salt    springs,    while    immense 
quantities  in  solution  give  its  characteristic  saltness  to  the 
sea. 

The  uses  of  this  substance  are  important :  not  among 
those  least  important  is  its  use  in  the  manufacture  of  the 
other  sodium  compounds,  especially  of  sodium  carbonate. 

230.  Manufacture  of  Sodium  Carbonate.  —  Enormous 
quantities  of  sodium  carbonate  are  used  in  bleaching,  soap- 
making,  glass-making,  and  other  arts.     The  several  processes 
in  its  manufacture  are  as  follows  :  — 

Sodium  Chloride  changed  to  Sodium  Sulphate.  -  - 
When  salt  is  heated  with  sulphuric  acid  in  a  reverberatory 
furnace,  mutual  decomposition  takes  place.  Sodium  sulphate 
and  hydrochloric  acid  are  the  products  of  the  reaction.  This 
may  be  understood  by  the  equation  :" — 

2NaCl  +  H2SO4  =  Na^SO*  +  2HC1. 

The  sodium  sulphate  thus  formed  is  valuable,  aside  from 
its  use  in  making  the  carbonate.  It  is  well  known  under  the 
name  of  GLAUBER'S  SALTS.  In  the  manufacture  now  being 
described,  it  is  called  SALT  CAKE. 

The  Sodium  Sulphate  changed  to  Sodium  Sulphide. 


CHEMISTRY.  219 

—  When  sodium  sulphate  is  decomposed  by  carbon,  the 
following  reaction  occurs  :  — 

Na2S04  +  4C  =  Na2S  -f  4CO. 

Sodium  sulphide  and  carbonic  oxide  are  produced.  In  the 
manufacture  of  sodium  carbonate,  the  sulphate,  with  small 
coal  and  chalk,  or  limestone  (calcium  carbonate),  are  thor- 
oughly mixed  and  melted  together  in  a  furnace.  The  above 
reaction  takes  place. 

The  Sodium  Sulphide  changed  to  Sodium  Car- 
bonate. —  The  sulphide  formed  by  this  reaction  is  at  once 
changed  by  the  calcium  carbonate  according  to  the  following 
equation :  — 

Na2S  +  CaC03  =  Na2CO3  +  CaS. 

Sodium  carbonate  and  calcium  sulphide  are  formed.  The 
mixture  has  a  blackish-gray  color,  and  is  called  BLACK  ASH. 

The  black  ash  is  afterward  thoroughly  leached  ;  during  this 
process  the  water  dissolves  out  the  carbonate,  but  leaves  the 
sulphide ;  and  then,  finally,  the  solution  is  evaporated  to 
dryness  :  the  residue  is  the  crude  sodium  carbonate  of  com- 
merce, generally  known  as  SODA  ASH. 

231.  Acid    Sodium    Carbonate.  —  Hydrosodium     car- 
bonate (bicarbonate  of  soda)  is  obtained  by  exposing  sodium 
carbonate  to  the   action  of  carbonic  acid.      Its   formula  is 
H  Na  C  O3.     This    is    the    substance    familiarly   known    as 
SODA,   and  used  so  commonly  instead  of   yeast  in   bread- 
making.     It  is  used  in  medicine :  it  is  also  much  used  in 
making  effervescing  drinks. 

SECTION  III. 

METALS  OF  THE  ALKALINE  EARTHS. 

232.  General  Description.  —  The  metals  of  the  second 
class  are  bivalent.     They  form   carbonates  which  are  not 


220 


CHEMISTRY. 


soluble  in  water,  unless  it  contains  carbonic  acid :  in  this 
respect  they  differ  from  the  metals  of  the  first  class.  The 
metals  themselves  are  of  little  use.  but  some  of  the  com- 
pounds of  calcium  and  barium  are  of  considerable  importance. 
Illustrations  of  these  Class  Properties.  —  The  metals 
of  this  class,  like  those  of  the  first,  decompose  water  at  all 
temperatures,  but  the  reaction  is  somewhat  different.  If 
calcium  is  used  for  the  purpose  of  illustration,  it  will  be : 

H2O  +  Ca  =  CaO  +  H2. 

Observe  that  one  combining  weight  of  calcium  replaces 
the  two  combining  weights  of  hydrogen  in  water.  This 
illustrates  the  bivalent  character  of  calcium :  the  other 
members  of  the  group  are  also  bivalent. 

The  calcium  oxide  (lime) ,  shown  in  the  reaction  just  given, 
combines  with  water,  evolving  much  heat,  actually  boiling  the 


Fig.  94. 


water  (Fig.  94)  to  form  the  calcium  hydrate    (slaked  lime), 
which  is  very  slightly  soluble  in  water,  forming  LIME-WATER. 


CHEMISTRY.  221 

233.  Calcium  Oxide.  —  The  oxide  is  made  on  a  large 
scale,  to  be  used  in  making  mortar  and  cements,  so  valuable 
in  building.     For  this  purpose  fragments  of  limestone  are 
mixed  with  coal  and  burned  in  kilns.     The  carbonic  acid  of 
the  limestone  is  driven  off  by  the  heat ;  and  the  other  con- 
stituent, lime,  or,  as  it  is  often  called,  QUICKLIME,  is  left, 
still  in  the  form  of  hard  and  compact  stone.     In  contact  with 
water  the  stone  swells,  grows  intensely  hot,  and  crumbles  to 
powder.     The  slaked  lime  thus  made  is  mixed  with  sand  to 
form  MORTAR. 

234.  Calcium  Carbonate.  —  The  members  of  this  group 
form  carbonates.     Limestone  and  marble  of  every  kind  are 
composed  chiefly  of  calcium  carbonate.     This  compound  is 
very  slightly  soluble   in  water  unless   it   contains  carbonic 
acid,  but  in  water  charged  with  this  gas  it  dissolves  readily. 
The  formation  of  STALACTITES  is  a  beautiful  illustration  of 
this   action.      Water,    charged   with    carbonic   acid,   flowing 
through  soil  and  over  rocks  where  limestone  is  abundant, 
dissolves  this  substance.      Finding   its  way  to   caverns,   it 
falls,  drop  by  drop,   from  the  roof.     Exposed   to   the   air, 
carbonic  acid  evaporates ;  the  water  can  no  longer  hold  the 
carbonate    in    solution,    but   deposits   it   wherever   it   rests. 
Drop  by  drop,  for  a  moment  clinging  to  the   roof,   leaves 
its   mite   of   carbonate   behind,   until  pendent   masses,   like 
icicles,  sometimes  of  curious  shape  and  beauty,  are  formed. 
The  carbonate  forms,  at  the  same  time,  on  the  bottom  of  the 
cave,  upright  masses  called  STALAGMITES. 


SECTION  IV. 
METALS  OF  THE  EARTHS. 

235.  General  Description.  —  Aluminium  is  the  most 
important  metal  of  the  third  class.  The  others  are  metals 
lately  discovered  by  means  of  the  spectroscope,  —  indium  in 


222  CHEMISTRY. 

1863,  and  gallium  in  1875.     These  metals  decompose  water 
at  high  temperatures,  and  form  sesquioxides  with  its  oxygen. 

236.  Aluminium.  —  This  element  has  a  combination  of 
properties  which  renders  it  one  of  the  most  interesting  in  the 
whole  series  of  metals.     It  has  the  hardness  and  luster  of 
silver  ;  and,  since  it  does  not  tarnish  when  exposed  to  air  and 
vegetable  acids,  it  would  seem  to  be  fitted  for  the  practical 
uses  to  which  silver  is  put.     It  melts  only  at  a  high  tempera- 
ture, and  may  then  be  cast  into  any  desired  form.     This, 
together  with  its  malleability,  ductility,  and  tenacity,  would 
enable  it  to  replace  iron  for  many  purposes,  while  its  lightness 
(density  2.56)  and  beauty  give  it  advantage  over  that  metal. 

Occurrence  in  Nature.  —  In  connection  with  these  valu- 
able properties  we  find  that  aluminium  is  one  of  the  most 
abundant  elements  in  nature.  It  is  a  constituent  of  clay  and 
marl,  of  slate,  and  indeed  of  most  rocks  and  soils.  It  must 
constitute  about  one- twelfth  of  the  solid  parts  of  the  earth. 

But  no  cheap  method  of  extracting  the  metal  is  yet  known, 
and  the  expense  stands  in  the  way  of  its  application  in  the 
arts.  It  is  now  manufactured  on  a  commercial  scale  in  Eng- 
gland  and  France,  and  it  has  been  used  for  ornamental  work 
and  in  making  physical  apparatus  where  strength  and  light- 
ness are  required. 

237.  Compounds.  —  The  most  important  compounds  of 
this  metal  are  aluminium  sulphate  and  alum.     The  formula  of 
the  first  is  A12  (S  O4)3.     It  is  largely  used  in  calico-printing. 

Alum  is  a  double  salt :  it  contains  the  metals  po- 
tassium and  aluminium,  both  as  sulphates.  Its  formula  is 
K2  A12  (S  O4)4  +  24  H2  O,  and  its  chemical  name  is  potassio- 
aluminium  sulphate.  The  water,  24  H2  O,  is  held  in  its  crys- 
tals, and  is  called  its  "  water  of  crystallization."  Heat  a 
few  crystals  of  alum,  and  this  water  will  be  expelled :  the 
alum  will  remain  bulky,  white,  and  opaque  ;  it  is  then  called 
"  burnt  alum." 

Other   metals   beside   potassium    may   combine   with   the 


CHEMISTRY.  223 

aluminium,  as  sulphates,  and  other  kinds  of  alum  are  thus 
produced.  Thus  common  alum  is  a  potassium  alum.  So 
also  we  have 

Na2Al2(SO4)4  .   .   .  Sodium  alum, 
(NH4)2A12  (SO4)4  .   .   .  Ammonium  alum. 


SECTION   V. 
METALS  OF  THE  ZINC  CLASS. 

238.  General  Description.  —  The  metals  of  this  class 
are  alike  fusible  at  quite  low  temperatures,  volatile  at  tem- 
peratures at  or  below  a  bright  red  heat,  and  combustible 
when  heated  in  the  air.  They  are  bivalent,  and  form,  each, 
but  one  oxide,  chloride,  and  sulphide.  They  decompose 
water  at  high  temperatures,  and  dilute  acids  at  low  tempera- 
tures, liberating  hydrogen  gas. 

Illustrations  of  the  Class  Properties.  —  The  melting- 
points  of  these  metals  are  comparatively  low ;  of  zinc  at 
423°  C.,  of  magnesium  a  little  higher,  and  of  cadmium  a 
trifle  lower. 

Heated  to  a  bright  red  heat,  magnesium  is  changed  to 
vapor ;  at  a  low  red  heat  cadmium  vaporizes,  and  zinc  at  a 
temperature  between  these  extremes. 

At  a  red  heat  in  the  air  these  metals  burn.  Cadmium 
gives  the  vapors  of  its  oxide  ;  zinc,  with  a  blue  flame,  form- 
ing clouds  of  vapor ;  and  magnesium,  with  a  flame  of  most 
dazzling  brightness,  sometimes  used  as  a  source  of  light  in 
photography  and  in  optical  experiments. 

At  high  temperatures  they  decompose  water,  and  form 
oxides.  In  this  reaction  one  atom  of  metal  replaces  two  of 
hydrogen,  and  forms  an  oxide  with  the  one  atom  of  oxygen  ; 
and  hence  they  are  bivalent. 

On  contact  with  sulphuric  or  hydrochloric  acid  they  dis- 
place the  hydrogen,  and  form  salts.  Indeed,  by  this  action 
of  zinc  we  have  seen  that  hydrogen  is  generally  prepared.. 


224  CHEMISTRY. 

239.  Zinc.  —  Zinc  blende  (a  sulphide),  calcimine  (a  car- 
Donate),  and  the  red  oxide,  are  the  ores  of  zinc  found  most 
abundantly ;  and  from  these  the  metal  is  extracted.     When 
either  of  the  first  two  is  used,   it  is  first  roasted,   that  is, 
heated  in  presence  of  air.     By  this  means  it  is  changed  to 
the  form  of  oxide.     The  oxide  is  then  mixed  with  coal,  and 
heated  in  a  close  vessel  having  an  iron  tube  reaching  ovet 
into  a  cold  receiver.      The  oxide   is  decomposed  ;    and  its- 
zinc,  in  the  form  of  vapor,  goes  over  to  be  condensed  in  the 
receiver. 

Properties  of  Zinc.  —  Zinc  is  a  bluish- white  metal,  about 
seven  times  (6.9)  as  heavy  as  water. 

At  low  temperature  zinc  is  brittle  ;  heated  to  about  200°  0- 
it  is  also  very  brittle  ;  but  between  these  extremes  (130°  C- , 
;  is  malleable,  and  is  rolled  or  hammered  into  thin  sheets  for 
various  uses. 

Zinc  is  not  easily  acted  upon  by  air,  and  on  this  account 
it  is  sometimes  used  as  a  coating  to  protect  iron  from  rust. 
Iron  covered  with  a  thin  coating  of  zinc  is  said  to  be  galvan~ 
ized. 

SECTION  VI. 

METALS  OF  THE  IRON  CLASS. 

240.  General  Description.  —  In  this  group  we  find  iron, 
manganese,  nickel,  and  cobalt.     The  last  three  named  more 
or  less  resemble  iron,  both  in  physical  and  chemical  proper- 
ties.    It  need  3  the  intense  heat  of  the  furnace  to  melt  iron  : 
the  same  is  true  of  the  others.     Even  at  so  high  a  tempera- 
ture iron  does  not  volatilize  :  neither  do  the  others.     Iron  is 
generally  bivalent,  but  sometimes  quadrivalent :  so  are  the 
rest ;  and  each  forms  several  oxides,  sulphides,  and  chlorides. 
Like  the  preceding  class,  these  metals  decompose  water  at 
high  temperatures,  and  acids  without  the  application  of  heat. 

241.  Iron.  —  Pure  metallic  iron  is  of  very  rare  occurrencf 


CHEMISTRY. 


225 


m  nature.  The  metal  is  found,  however,  in  great  abundance 
in  combination  with  non-metals  ;  its  oxides  and  its  sulphides 
being  the  most  common  ores.  The  magnetic  oxide  occurs  in 
large  quantities  in  many  parts  of  the  United  States,  and  is 
used  extensively  in  the  manufacture  of  the  metal.  It  is  the 
ore  from  which  the  best  "  Swedish  iron  "  is  also  made.  In 
England  an  impure  carbonate,  called  argillaceous  iron-ore,  is 
chiefly  used. 

The  iron  of  commerce  occurs  in  three  forms,  —  cast-iron, 
wrought-iron,  and  steel. 

Cast-iron  is  a  compound  of  iron  with  small  and  variable 
quantities  of  carbon.  It  is  obtained  from  the  ores  by  heating 
them  in  a  blast-furnace. 

Wrought-iron  is  nearly  pure  iron,  but  still  contains  a  very 
small  proportion  of  car- 
bon. It  is  obtained  gen- 
erally from  cast-iron  by 
burning  out  its  carbon 
in  a  reverberatory  fur- 
nace. 

Steel  is  also  a  com- 
pound of  iron  and  car- 
bon, containing  less  car- 
bon than  cast-iron,  but 
more  than  wrought-iron. 
It  is  made  from  cast-iron 
by  burning  out  its  car- 
bon, or  from  wrought- 
iron  by  adding  carbon 
to  it. 


242.  Cast  Iron.  —  In 

the  most  ancient  of  his- 
tories we  read  of  Tubal- 


Fig.  95. 


Cain,  who  was  the  great-grandson  of  the  son  of  Adam.     We 
are  told  that  he  was  a  cunning  workman  in  brass  and  iron, 


226 


CHEMISTRY. 


Even  in  such  early  days  this  metal  must  have  been  extracted 

from  its  ores. 

The  ores  are  reduced  by  heat  in  a  blast-furnace. 

The  Blast-Furnace.  —  The  exterior  of  a  blast-furnace  is 

shown  in  Fig.  95.  This,  together  with  Fig.  96,  which  repre- 
sents a  section  of  it, 
will  enable  us  to  explain 
its  construction.  The 
interior  has  the  shape 
of  a  double  cone.  It 
is  built  of  the  most  in- 
fusible fire-brick,  and 
inclosed  in  solid  mason- 
ry. It  is  very  large, 
perhaps  fifty  feet  high 
by  fifteen  feet  in  width 
at  its  widest  part.  The 
bottom  is  closed,  and 
the  air  needed  for  the 
fire  is  forced  by  steam- 
engines  through  pipes, 
T.  The  fuel  and  the 
ore,  with  broken  lime- 
stone or  other  flux,  are 


Fig.  96. 


put  in  at  the  top :  the  metal  is  drawn  off  at  the  bottom. 

The  Process.  —  The  ore,  if  necessary,  is  first  roasted,  by 
which  it  is  changed  to  the  form  of  oxide.  The  oxide  mixed 
with  fuel  and  flux  is  made  to  fill  the  furnace.  The  fire,  having 
been  started,  is  kept  up  by  the  blast  of  hot  air  (a  cold  blast 
sometimes)  driven  by  the  engine.  "  Where  the  blast  first 
touches  the  burning  fuel,  carbon  dioxide  is  formed :  this  gas, 
with  nitrogen,  rising  through  the  furnace,  comes  in  contact 
with  white-hot  carbon,  and  is  reduced  to  carbon  oxide.  The 
layers  of  solid  material  thrown  in  at  the  top  of  the  furnace 
gradually  sink  down  ;  and,  as  soon  as  a  stratum  of  ore  has 
gone  far  enough  to  be  heated  by  the  hot  mixture  of  nitrogen 


CHEMISTRY.  227 

and  carbon  oxide,  it  becomes  reduced  to  spongy  metallic 
Iron,  which,  mixed  with  flux  and  the  earthy  impurities  of  the 
ore,  settles  down  to  hotter  parts  of  the  furnace,  where  it 
enters  into  a  fusible  combination  with  carbon,  while  the  flux 
and  earthy  impurities  melt  together  to  a  liquid  slag.  The 
liquid  carburetted  iron  settles  to  the  very  bottom  of  the 
furnace,  whence  it  is  drawn  out  at  intervals  through  a  tap- 
ping-hole, which  is  stopped  with  sand  when  not  in  use." 
(Eliot  and  Storer.) 

The  Dra  wing-off. —  In  front  of  the  furnace  is  a  large 
level  bed  of  sand.  A  channel  is  scooped  through  the  middle 
of  this  bed,  and  it  reaches  all  the  way  from  the  bed  to  the 
hearth  of  the  furnace.  From  the  large  channel  in  the  mid- 
dle of  the  bed  of  sand,  there  are  smaller  ones  reaching  out 
each  side,  and  then  from  these  there  are  other  branches 
about  three  feet  long  and  three  or  four  inches  wide.  Look 
at  the  picture  (Fig.  95),  and  you  will  see  the  arrangement  of 
this  central  channel  with  its  branches. 

Now,  about  every  twelve  hours  the  furnace  is  opened  at  the 
bottom  for  the  melted  metal  to  run  out.  It  has  no  choice  of 
places  :  it  must  flow  down  through  the  large  channel,  and  off 
into  all  the  branches  in  the  bed  of  sand.  There  it  is  allowed 
to  cool. 

The  iron  thus  obtained  is  the  cast-iron  of  commerce.  The 
short  bars  cast  in  the  sand  are  known  as  pigs.  Indeed,  the 
crude  cast-iron  from  the  blast-furnace  is  often  called  PIG- 
IRON. 

243.  Casting.  —  Large  quantities  of  cast-iron  are  used 
for  various  purposes.  In  order  to  make  it  into  useful  articles 
it  is  melted,  and  the  liquid  metal  is  poured  into  molds, 
This  operation  is  called  CASTING.  The  melting  of  the  iron  is 
accomplished  in  what  is  called  a  CUPOLA  FURNACE. 

The  Cupola  Furnace.  —  This  furnace  is  built  of  fire- 
bricks, and  incased  in  iron.  It  is  several  feet  high,  and 
cylindrical,  with  a  door  at  some  distance  above  the  bottom 


228 


CHEMISTRY. 


for  the  iron  and  fuel  to  be  put  in,  and  a  hole,  known  as  the 
tap-hole,  at  the  bottom,  for  the  melted  metal  to  run  out. 

In  the  first  place,  molds  of  the  desired  article  are  made  in 
sand. 

Then,  when  the  melted  cast-iron  is  ready  in  the  furnace, 
the  tap-hole  is  opened.  A  fiery  stream  of  liquid  iron  pours 
out :  it  is  caught  in  ladles  by  the  workmen,  who  hurry  it 
away  to  the  molds.  The  fluid  metal  runs  into  every  little 
groove  and  corner  of  the  mold,  and  there  hardens  into  the 
desired  form. 

244.  Wrought-Iron.  —  Wrought- iron  is  the  purest  form 
of  commercial  iron,  and  is  generally  obtained  by  treating 
cast-iron  in  a  reverberatory  furnace. 

The  Reverberatory  Furnace.  —  A  section  of  a  rever- 
beratory furnace  is  shown  in  Fig.  97.  The  cast-iron  is 


Fig.  97. 

placed  at  D  upon  the  hearth.  The  fire,  A,  is  separated  from 
the  hearth  by  a  wall  of  fire-brick.  The  roof  is  arched  down- 
ward to  the  chimney,  which  is  forty  or  fifty  feet  high,  to 
cause  a  strong  draught. 

The  Process.  —  Flame  and  hot  gases  from  the  fire,  strik- 
ing against  the  arched  roof,  are  reflected  down  upon  the  cast- 


CHEMISTEY.  229 

iron.  In  a  little  time  the  iron  begins  to  melt.  When  it  has 
been  all  reduced  to  a  pasty  state,  the  furnace-man  unstops 
an  opening  (B),  through  which  he  puts  his  paddle.  By 
thoroughly  stirring  (puddling)  the  pasty  mass,  all  parts  are 
brought  in  contact  with  the  hot  air,  during  which  a  part  of 
its  impurities,  in  the  form  of  slag  or  scoria,  is  allowed  to 
run  off,  while  its  carbon  is  burned,  and  its  gas  escapes  to  the 
chimney.  The  metal  is  then  formed  into  balls,  taken  from 
the  furnace,  pressed  or  hammered  to  remove  the  remaining 
scoria,  and  then  rolled  into  bars  or  other  forms  of  WROUGHT 
or  MALLEABLE  IRON. 

245.  Steel.  —  The  difference  between  steel  and  both  cast- 
iron  and  wrought-iron  is  in  the  quantity  of  carbon  it  contains. 
It  contains  less  than  cast-iron  and  more  than  wrought-iron. 
Formerly  steel  was  made  by  adding  carbon  to  wrought-iron  : 
lately  it  is  largely  made  by  taking  a  part  of  its  carbon  from 
cast-iron. 

Steel  from  Cast-Iron.  —  From  two  to  six  tons  of  cast- 
iron,  when  melted,  is  run  into  a  large  globular  vessel,  built 
of  the  most  infusible  substance.  Numerous  holes  in  the 
bottom  of  this  crucible  allow  a  strong  blast  of  air  to  bubble 
up  through  the  melted  metal.  A  most  violent  combustion 
follows,  the  heat  of  which  keeps  the  metal  in  a  fluid  state, 
while  its  carbon  and  a  small  part  of  the  metal  itself  are 
burned  to  oxides.  Too  much  carbon  is,  by  this  process,  re- 
moved, and  a  quantity  of  cast-iron  is  added  to  restore  carbon 
enough  to  change  the  whole  mass  into  steel.  The  crucible  is 
then  tipped  upon  its  pivots,  and  the  melted  steel  run  off  into 
molds.  Less  than  half  an  hour  is  enough  to  change  these 
tons  of  cast-iron  into  cast-steel.  The  process  is  known  as 
the  BESSEMER  PROCESS. 

From  Wrought-iron.  —  The  older  method  of  prepar- 
ing steel  is  called  "  cementation."  Bars  of  wrought-iron, 
embedded  in  charcoal  and  inclosed  in  boxes  from  which  air  is 
very  carefully  excluded,  are  heated  to  redness,  and  kept  in 


230  CHEMISTRY. 

this  condition  for  several  days.  A  curious  and  obscure 
chemical  action  goes  on,  by  which  these  two  solid  substances 
unite,  —  the  carbon  penetrating  and  combining  with  all  parts 
of  the  iron,  and  thus  changing  it  to  steel.  To  make  its 
composition  uniform,  this  "  blistered  steel,"  as  it  is  called, 
is  melted,  and  cast  into  large  but  short  bars  called  ingots. 


SECTION  VII. 

METALS  OF  THE  TIN  CLASS. 

246.  General  Description.  —  Tin    is    the    only   useful 
metal  of  its  class.     The  others  resemble  tin  in  their  chemical 
properties,  but  they  are  rare  and  unimportant.     These  metals 
are  quadrivalent,  and  decompose  water  at  high  temperatures, 
forming  dioxides. 

247.  Tin.  —  Tin  is  not  an   abundant  element  in  nature, 
and  yet  it  is  one  of  the  metals  longest  known  to  men.     The 
mineral  called  tinstone  (stannic  oxide,  Sn  O2)  is  the  chief 
source  of  the  metal.     Mixed  with  powdered  coal  and  a  little 
lime,  the  ore  is  spread  upon  the  hearth  of  a  reverberatory 
furnace.     The  carbon  takes  the  oxygen  from  the  ore,  and 
the  melted  metal  is  run  off  into  iron  molds. 

In  color  tin  resembles  silver.  It  is  soft,  malleable,  and 
ductile. 

Tin  does  not  easily  lose  its  luster  by  exposure  to  air,  and 
on  this  account  it  is  largely  used  as  a  covering  for  other 
metals :  common  tin-ware  is  sheet-iron,  which  has  been 
covered  with  a  thin  coating  of  tin. 

SECTION  VIII. 

METALS  OF  THE  ANTIMONY  CLASS. 

248.  General  Description.  —  Of  this  class  arsenic,  anti- 
mony, and  bismuth  are  the  most  important  metals.     They 


CHEMISTRY.  231 

are  trivalent,  and  are  very  closely  related  to  the  trivalent 
group  of  non-metals.  In  bismuth  the  metallic  character  is 
very  clear,  in  antimony  it  is  less  evident,  in  arsenic  it  is  very 
doubtful,  and  in  phosphorus  and  nitrogen  it  is  altogether 
absent.  From  bismuth  to  nitrogen,  the  transition  from  metal 
to  non-metal  is  gradual  and  perfect. 

249.  Arsenic.  —  This  element  has  been  already  described 
as  a  non-metal,  and  its  relation  to  nitrogen   and  phosphorus 
pointed  out.     On  the  other  hand,  it  is  related  to  antimony  and 
bismuth,  whose  metallic  character  is  more  decided.     It  would 
seem  to  be  the  bond  which  links  these  two  divisions  of  the 
elements  together. 

250.  Antimony.  —  Like  arsenic,  antimony  combines  with 
three  atoms  of  hydrogen  to  form  a  combustible  gas.     Treated 
in  Marsh's  apparatus,  it  also  forms  a  stain  upon  white  porce- 
lain,  or  a   metallic   mirror  in   the   tube.     So   great   is   the 
resemblance  between  the   stains   of   antimony  and   arsenic, 
that  care  is  to  be  used  not  to  confound  the  two  metals  in  the 
test.     The  antimony  stain  is  known  by  its  more  feeble  luster, 
its  blackness,  and  the  high  heat  needed  to  volatilize  it. 

Its  most  Useful  Alloy.  —  Antimony,  with  tin  and  lead, 
are  melted  together  to  make  type-metal,  the  most  useful  of  all 
alloys,  since  the  art  of  printing  depends  upon  its  use.  It 
has  the  curious  property  of  expanding  when  it  cools  from 
the  melted  liquid  to  the  solid  form.  On  this  account,  when 
poured  into  the  type-molds,  and  allowed  to  become  cold,  it 
fills  every  little  groove  and  marking  of  the  mold,  and  thus 
takes  the  perfect  shape  of  the  type. 

251.  Bismuth.  —  Bismuth   forms   oxides    and    chlorides 
whose   composition   is   analogous   to   those   of  arsenic   and 
antimony.     It  is  trivalent,  like  the  others. 

The  metal  itself  is  of  a  reddish  hue,  and,  like  the  other 
two,  very  brittle.  It  melts  at  264°  C.  (507°  F.)  ;  and,  when 
cooling,  it  crystallizes  and  expands. 


232  CHEMISTRY. 

With  other  metals  bismuth  forms  alloys  remarkable  for  the 
low  temperature  at  which  they  melt.  Its  alloy  with  lead  and 
tin  (two  parts  bismuth,  one  of  lead,  and  one  of  tin)  is  called 
"fusible  metal :  "  it  melts  at  93°  7 C.  (200°  F.) .  This  alloy 
is  used  for  taking  casts  from  medals  and  dies  :  on  cooling,  it 
expands,  and,  filling  every  crevice  or  line  of  the  die,  makes 
a  most  beautiful  and  faithful  copy. 

SECTION  IX. 

METALS  OF  THE  LEAD  CLASS. 

252.  General  Description.  —  This    class   contains   only 
two  metals,  lead  and  thallium.     Lead  has  been  known  from 
the  earliest  times  :  thallium  has  been  known  only  since  1861. 
They  are  alike  in  being  soft  enough  to  yield  to  pressure  by 
the  finger-nails  ;  in  being  fusible  below  red  heat ;  in  being 
malleable  and  ductile ;  and  in  being  heavy  metals,  lead  11.2 
and  thallium  11.8  heavier  than  water. 

In  their  chemical  properties  these  metals  do  not  so  per- 
fectly agree.  Lead  is  bivalent :  thallium  is  univalent.  In 
other  respects,  also,  thallium  resembles  the  alkaline  metals. 

253.  Lead.  —  The  ore  from  which  the  lead  of  commerce 
is  obtained  is  a  sulphide  (Pb  S),  called  galena.     The  color 
and  luster  of  this  ore  are  much  like  that  of  the  metal  itself, 
but  the  ore  is  much  harder.     It  is  crystalline,  and  sometimes 
occurs  in  cubes  of  the  most  perfect  form. 

To  obtain  metallic  lead,  galena  is  mixed  with  lime,  and 
roasted  in  a  reverberatory  furnace.  By  this  means,  a  part  of 
the  ore  is  changed  to  oxide,  another  part  to  sulphate,  and 
some  remains  a  sulphide  as  it  was.  The  air  is  then  shut  off 
from  the  furnace,  and  the  heat  raised :  the  compounds  are 
then  all  decomposed,  and  metallic  lead  is  produced. 

Its  Uses.  —  Metallic  lead  has  numerous  and  important 
uses.  Among  them  we  may  especially  notice  the  construc- 
tion of  water-pipes  and  cisterns.  In  cities  supplied  with 


CHEMISTRY.  233 

water  from  reservoirs,  the  conduit-pipes  are  almost  univer- 
sally made  of  lead. 

Action  of  Lead  upon  Water.  —  But,  since  the  com- 
pounds of  lead  are  poisonous,  the  chemical  action  of  lead 
upon  water  is  a  matter  of  great  importance.  Together, 
especially  in  the  presence  of  air,  they  form  an  oxide  which 
is  somewhat  soluble  in  water.  But  this  corrosive  action  is 
very  much  modified  by  the  presence  of  impurities.  It  is 
increased  by  ammonium  nitrate :  it  is  diminished  by  sul- 
phates and  carbonates. 

Water  containing  a  solution  of  calcium  carbonate  scarcely 
affects  the  lead,  because  an  insoluble  carbonate  is  formed  on 
the  surface  of  the  metal  which  prevents  any  further  action ; 
but,  if  it  contains  much  free  carbonic  acid,  this  removes  the 
lead  carbonate,  which  otherwise  would  protect  the  surface, 
and  leaves  the  metal  of  the  pipes  constantly  exposed  to  cor- 
rosion. 

Whether  drinking-water  may  be  kept  in  lead  cisterns  and 
pipes  without  risk  to  health,  depends  on  the  character  of  the 
water  ;  and  the  question  can  be  decided  only  by  learning  what 
substances  the  water  holds  in  solution,  and  what  is  their 
chemical  action  on  the  metals. 


SECTION  X. 

METALS  OF  THE  SILVER  CLASS. 

254.  General  Description. — The  members  of  this  class, 
copper,  mercury,  and  silver,  are  sometimes  found  native,  but 
they  are  much  more  abundant  in  combination.     Their  sul- 
phides are  their  most  common  ores.     They  can  not  decom- 
pose water  at  any  temperature.     Copper  and  mercury  are 
bivalent,  but  silver  is  univalent. 

255.  Copper.  —  Free   metallic   copper   is    found    in   the 
noted  mines  of   Cornwall  and  Devon,  in  England,  and  in 
many  other  parts  of  Europe.     But  some  of  the  finest  native 


234  CHEMISTRY. 

copper  in  the  world  is  found  in  the  region  of  Lake  Superior. 

One  single  mass  of  Lake  Superior  copper  weighed  over  400 

tons. 

The  native  copper  has  very  curious  crystalline  forms.     In 

some  cases  it  is  found  in  little  cubes.     In  some  cases  the 

small  crystals  are  grown  to- 
gether  in  vast  numbers,  and 
tmis  make  large  masses  ; 
MI  i<  1  these  masses  often  show 
the  most  sinular  branch- 


Fig.  98. 

tempting  one  sometimes  to 
fancy  that  the  metal  had  tried  to  imitate  the  form  of  some 
growing  plant. 

Ores  of  Copper.  —  Copper  pyrites  is  the  most  abundant 
ore  of  this  metal.  To  a  great  deal  of  this  ore  nature  has 
given  the  form  of  beautiful  cubes,  having  a  color  and  luster 
something  like  brass.  This  ore  is  composed  of  copper,  iron, 
and  sulphur,  Cu  Fe  S2. 

Besides  this,  there  are  other  sulphides  of  copper,  Cu2  S, 
and  Cu  S.  The  oxides  also  are  abundant  ;  so  also  are  the 
carbonates.  Malachite  is  one  of  these. 

Malachite  is  a  rich  ore  of  copper,  but  much  less  common 
than  many  others.  It  is  a  stone  of  most  beautiful  color. 
Its  rich  green  surface  also  takes  a  fine  polish,  and  on 
these  accounts  it  is  often  used  for  purposes  of  ornament. 
It  is  a  compound  of  copper,  represented  by  the  formula 
CuCO3  +  Cu  (HO),. 

Smelting  the  Ores.  —  To  obtain  the  metal,  the  ores  of 
copper  are  first  roasted  and  afterward  melted.  These  opera- 
tions are  repeated  until  the  mass  contains  only  two  com- 
pounds of  the  metal,  the  oxide  and  the  sulphide. 

The  mass  is  then  again  roasted  ;  and,  during  this  heating, 
the  two  compounds  attack  each  other.  The  sulphur  of  one 
and  the  oxygen  of  the  other  are  taken  away,  leaving  the 
copper  of  both  in  metallic  form. 


CHEMISTRY. 


235 


Refining".  —  This  crude  copper  from  the  ore  contains  other 
metals  which  must  be  removed.  The  process  of  "  refining  " 
is  for  this  purpose.  It  consists  in  re-melting  the  metal,  and 
keeping  it  in  the  fluid  form,  exposed  to  air,  for  several  hours. 
By  this  means  the  impurities  are  oxidized  or  burned  out. 
The  molten  copper  is  then  taken  from  the  furnace  in  ladles, 
and  poured  into  molds,  which  give  it  the  form  of  solid  bars. 


Fig.  99. 

The  furnace,  and  some  of  these  last  operations,  are  shown  in 
Fig.  99. 

Properties  of  the  Metal.  —  Copper  is  a  red  metal,  very 
tenacious,  very  ductile,  and  malleable. 

Copper  is  among  the  very  best  conductors  of  electricity, 
and  is  much  used  in  the  construction  of  electrical  apparatus 
and  lightning-rods. 

It  slowly  tarnishes  in  the  air,  and  is  readily  acted  upon  by 
vegetable  acids  :  the  compounds  formed  are,  many  of  them, 
poisonous.  On  this  account  copper  vessels  to  be  used  for 
culinary  purposes  are  usually  coated  with  tin. 


236  CHEMISTEY. 

Alloys  of  Copper.  — •-  Brass  is  an  alloy  of  copper  and 
zinc :  it  is  made  by  melting  together  two  parts  of  copper  to 
one  of  zinc. 

Bronze,  gun-metal,  and  bell-metal  are,  for  the  most  part, 
mixtures  of  copper  and  tin. 

German  silver  is  an  alloy  of  copper,  zinc,  and  nickel. 

256.  Mercury.  —  This  metal  was  known  in  very  ancient 
times ;  and  besides  mercury,  a  name  which  the  old  chemists 
gave  it,  this  lustrous  fluid  was  early  called  quicksilver,  and 
this  name  is  still  in  very  common  use. 

This  metal  is  found  in  California,  in  China,  in  Austria,  and 
to  some  extent  in  other  countries.  Perhaps  the  most  noted 
among  its  native  countries  is  Spain :  the  mines  of  Almaden 
in  that  country  have  long  been  worked,  and  have  yielded  a 
rich  reward. 

Mercury  is  generally  found  combined  with  sulphur.  This 
ore  is  called  cinnabar.  It  is  a  very  pretty  mineral,  much  the 
color  of  cochineal.  Sometimes  this  ore  is  so  pure  that  its 
color  is  as  rich  and  brilliant  as  that  of  vermilion.  Indeed, 
these  two  things  have  the  same  composition  :  cinnabar  is  the 
sulphide  which  is  found  in  the  earth ;  vermilion  is  the  sul- 
phide which  is  made  in  the  chemist's  laboratory.  Both  have 
the  composition  represented  by  the  formula  HgS. 

Reducing  the  Ore.  —  To  obtain  the  metal,  the  cinnabar 
is  roasted  in  a  furnace  with  plenty  of  air.  The  oxygen  of  the 
air  decomposes  the  ore,  and  combines  with  its  sulphur,  leaving 
its  mercury  free.  At  the  temperature  of  the  furnace  the 
metal  is  in  vapor.  This  vapor  is  carried  over  into  cold 
chambers,  where  it  condenses  to  liquid  form. 

Properties.  —  Mercury  is  a  liquid  metal  about  13.5  times 
heavier  than  water.  It  becomes  a  silver-white  solid  at 
-39. 6°  C.  (-39. 4°  F.). 

Mercury  forms  two  oxides,  the  mercurous,  Hg2O,  and  the 
mercuric,  Hg  O.  The  last-named  substance  is  a  red  powder, 
once  known  as  "red  precipitate,"  and  is  of  historic  inter- 


CHEMISTRY.  237 

est,  since  by  heating  it  Priestly  discovered  oxygen  in  the 
year  1774.  Nevertheless  mercury  and  oxygen  have  so  little 
attraction  at  ordinary  temperature,  that  the  surface  of  the 
metal  remains  bright  on  exposure  to  air. 

Its  attraction  for  chlorine  is  stronger :  the  two  combine  at 
ordinary  temperature.  Two  chlorides  are  well  known  :  they 
are  the  mercurous  chloride,  Hg2  C12,  and  the  mercuric  chloride, 
Hg  CU.  The  former  is  calomel,  so  long  and  largely  used  in 
medicine ;  and  the  latter  is  corrosive  sublimate,  a  virulent 
poison.  Both  are  white  solids  ;  yet  they  are  easily  distin- 
guished, because  corrosive  sublimate  is  soluble  in  water, 
while  calomel  is  not. 

Amalgams.  —  The  alloys  of  mercury  are  called  AMAL- 
GAMS. The  most  familiar  example  is  to  be  seen  on  the 
backs  of  mirrors  :  this  substance  is  an  amalgam  of  mercury 
and  tin. 

Uses. —  Metallic  mercury  is  largely  used  in  "silvering" 
mirrors,  in  the  construction  of  thermometers  and  barometers, 
and  also  in  extracting  silver  and  gold  from  their  ores. 

257.  Silver.  —  Silver,  like  the  other  metals  of  greatest 
use  in  the  arts,  is  very  widely  distributed.  It  is  found  native 
and  often  alloyed  with  mercury,  copper,  and  gold ;  but  its 
sulphide  (Ag2  S) ,  either  alone  or  mixed  with  other  metallic 
sulphides,  is  its  most  common  form.  From  these  ores  the 
metal  is  usually  obtained.  They  are  found  in  many  coun- 
tries of  Europe,  but  in  greater  abundance  and  richness  in 
Peru,  Mexico,  and  the  Pacific  slope  of  the  United  States. 

Obtained  by  Cnpellation. —  Galena  almost  always  con- 
tains silver,  and  often  in  quantities  which  make  it  valuable  for 
the  extraction  of  silver  as  well  as  lead.  "  It  has  been  found 
profitable  to  extract  the  silver  from  load  that  contains  less 
than  one-thousandth  of  its  weight  of  the  precious  metal." 
From  lead  rich  in  silver  this  metal  is  obtained  at  once 
by  cupellation;  but,  when  so  poor  as  that  just  described,  the 
lead  is  first  melted,  and  then,  while  cooling  slowly,  it  is 


238  CHEMISTRY. 

stirred.  As  it  cools,  it  crystallizes  ;  and  the  crystals  may  be 
dipped  out  of  the  liquid  mass  in  colanders.  Now,  an  alloy 
of  lead  and  silver  will  remain  melted  when  cooled  below  the 
temperature  at  which  pure  lead  solidifies.  Hence  the  crystals 
dipped  out  in  the  colander  are  crystals  of  lead,  while  all 
the  silver  remains  in  the  fluid  left  behind.  By  this  means  the 
proportions  of  lead  are  reduced  until  the  metal  is  rich  in 
silver,  after  which  it  is  cupelled. 

The  process  of  cupeUation  is  based  upon  the  fact  that  lead 
is  rapidly  oxidized  by  air  at  high  temperature,  while  silver  is 
not. 

The  alloy,  placed  in  a  shallow  porous  vessel  of  bone- 
earth,  called  a  cupel,  is  melted  in  a  furnace,  and  its  surface 
is  at  the  same  time  exposed  to  a  current  of  hot  air.  The 
lead  is  changed  to  an  oxide :  the  melted  oxide  is  partly 
absorbed  by  the  cupel,  while  another  part  runs  off  into  other 
vessels.  The  silver  is  not  affected  by  the  air  ;  and,  when  the 
lead  has  passed  away,  the  precious  metal  still  remains  in 
the  cupel. 

Obtained  by  Amalgamation.  —  From  other  ores  than 
argentiferous  lead,  silver  is  extracted  by  a  process  called 
amalgamation.  It  is  based  upon  the  fact  that  silver  is  very 
soluble  in  mercury. 

For  this  process,  also,  the  ores  require  a  preliminary  treat- 
ment. After  being  thoroughly  ground,  they  are  mixed  with 
common  salt,  and  then  roasted.  By  this  means  the  silver  is 
changed  to  a  chloride.  The  roasted  substance  is  then  mixed 
with  water  and  fragments  of  iron,  and  the  mixture  is 
violently  shaken  in  revolving  casks.  Mercury  is  soon  added, 
and  the  agitation  is  kept  up  for  perhaps  twenty  hours.  In 
the  mean  time  the  iron  decomposes  the  chloride,  and  the 
silver  thus  set  free  is  dissolved  at  once  in  the  mercury. 
The  excess  of  mercury  in  the  amalgam  is  removed  by  filter- 
ing it  through  leather  bags  under  pressure,  and  the  rest  by 
distillation.  The  precious  metal  is  left  behind. 
L  Properties,  —  Silver  is  the  whitest  of  metals.  It  is  very 


CHEMISTRY.  239 

malleable  and  ductile,  much  harder  than  gold,  and  ten  and  a 
half  times  heavier  than  water.  Its  surface  is  not  tarnished 
on  exposure  to  air,  not  even  when  heated  in  oxygen  ;  but 
it  quickly  blackens  on  exposure  to  sulphuretted  hydrogen, 
because  of  the  strong  attraction  between  silver  and  sulphur. 

Its  Alloys.  —  Silver  is  too  soft  for  most  purposes  in  the 
arts.  Small  quantities  of  other  metals  increase  its  hardness. 
For  coin  and  for  articles  of  plate,  it  is  alloyed  with  copper. 
The  English  standard  silver  contains  7.5  per  cent  of  copper. 
The  standard  is  regulated  by  law,  and  is  not  the  same  in  all 
countries.  In  the  United  States  the  legal  silver  coin  is  -f^ 
silver  and  -^  copper. 

258.  Action   of  Light  on    Silver   Compounds. — We 

have  seen  that  light  is  an  active  agent  in  many  chemical 
changes  :  we  may  add  that  the  salts  of  silver  are  especially 
sensitive  to  its  influence.  An  easy  experiment  can  be  made 
to  illustrate  this  fact. 

On  the  Chloride. —  Into  a  test-tube  put  a  quantity  of 
a  solution  of  silver  nitrate,  and  add  a  few  drops  of  hydro- 
chloric acid.  A  heavy  white  precipitate  of  silver  chloride 
is  at  once  formed,  which  speedily  settles  to  the  bottom.  Let 
the  tube  be  now  placed  in  the  sunlight,  and  an  interesting 
change  of  color  will  be  gradually  produced.  The  snow- 
white  chloride  becomes  pink,  violet,  brown,  and  at  last 
dark  bronze-black.  The  chloride,  dry  and  pure,  will  not 
show  this  change  on  exposure  to  light :  moisture  seems  to 
be  necessary.  Light  causes  a  reaction  between  water  and  the 
chloride,  by  which  hydrochloric  acid  is  formed,  and  a  small 
quantity  of  metallic  silver  is  set  free.  To  the  presence  of  this 
metal  in  a  state  of  very  fine  division  the  darkening  is  due. 

On  the  Nitrate.  —  Silver  nitrate  is  not  changed  by  the 
action  of  light  unless  in  contact  with  organic  matter :  it  then 
blackens  like  the  chloride. 

On  the  Oxide.  —  When  silver  iodide  is  exposed  to  light 
no  visible  change  occurs,  but  still  a  molecular  change  does 


240  CHEMISTRY. 

take  place.  This  curious  fact  may  be  shown  by  experi- 
ments. Let  two  highly  polished  plates  of  silver  be  held  in 
iodine  vapor  in  the  dark  :  by  this  means  a  thin  film  of  iodide 
will  be  made  over  their  surfaces.  Leave  one  plate  in  the 
dark,  and  put  the  other,  for  a  time,  in  the  sunlight :  the  two 
plates  still  look  alike  ;  the  light  has  caused  no  visible  change. 
But  now  hold  both,  in  a  box  at  moderate  temperature,  over 
the  vapor  of  mercury :  the  one  which  was  exposed  to  the 
light  immediately  blackens  ;  the  other  is  not  changed.  The 
darkening  in  this  case  is  due  tl)  a  combination  of  mercury 
with  the  silver  of  the  iodide,  —  the  mercury  decomposing  the 
iodide  after  exposure  to  the  light. 

The  nature  of  the  action  of  light  in  this  case  has  been  in 
doubt.  The  best  explanation  (Amer.  Jour,  of  Sci.,  vol.  42, 
p.  198,  and  vol.  44,  p.  71)  supposes  it  to  be  a  physical 
action,  by  which  the  molecules  are  so  disturbed  as  to  yield 
afterward  to  the  attraction  of  mercury.  That  is  to  say,  the 
molecules  of  the  iodide  are  so  shaken  by  the  impact  of  the 
waves  of  light  that  their  atoms  are  almost  ready  to  fall 
apart.  In  this  condition  the  attraction  of  the  mercury  for 
the  iodine  is  strong  enough  to  complete  the  decomposition. 

259.  Photography.  —  Photography  is  the  art  of  making 
pictures  by  means  of  light.     While  there  are  many  different 
processes,   each   requiring  different  substances  sensitive  to 
light,  still  the  most  interesting  process  is  the  one  so  univer- 
sally used  in  portraiture  ;  and  this  is  based  on  the  sensitive- 
ness of  the  compounds  of  silver. 

The  process  consists  of  two  parts  ;  viz.,  the  making  of  the 
negative,  and  then  the  making  of  a  positive. 

260.  Making  the  Negative.  —  Glass  is  employed  as  the 
substance  on  which  the  picture  taken  directly  from  the  object 
is  held.     But  in  order  to  use  it  the  surface  must  be  made 
sensitive  to  light. 

Preparation  of  the  Plate.  —  The  object  is  to  give  the 
glass  a  coating  which  contains  silver  iodide. 


CHEMISTRY.  241 

Cotton,  acted  on  by  a  mixture  of  nitric  and  sulphuric 
acids,  is  changed  to  gun-cotton,  or  pyroxyline  ;  and  this, 
when  dissolved  in  alcohol  and  ether,  forms  the  substance 
called  COLLODION.  A  small  quantity  of  an  iodide  (potassic), 
or  a  mixture  of  two  or  three  iodides,  is  put  with  the  collodion, 
and  the  solution  is  then  rapidly  poured  from  a  wide-mouthed 
vessel  over  the  very  clean  and  dry  surface  of  the  glass :  the 
alcohol  and  ether  quickly  evaporate,  and  leave  a  thin  film 
upon  the  glass,  which  is  then  plunged  into  a  bath  of  silver 
nitrate.  While  in  this  bath  for  a  few  minutes,  the  iodine  in 
the  film  takes  silver  from  the  nitrate,  and  forms  silver  iodide 
(Agl).  The  plate  being  taken  from  the  bath,  thoroughly 
washed  and  dried,  is  ready  to  receive  the  action  of  light. 

Exposure  in  the  Camera.  —  The  plate,  with  the  sen- 
sitive film  on  its  surface,  is  exposed  in  a  camera  for  a  short 
time,  during  which  the  light  from  the  object  performs  its 
curious  action  upon  the  iodide,  by  which  no  picture  is  made 
visible,  but  by  which  one  is  prepared  to  be  developed.  On 
pouring  over  the  film  of  iodide  a  solution  of  pyrogallic  acid 
(C0  H6  O3)  or  of  ferrous  sulphate  (Fe  S  O4) ,  containing  a  few 
drops  of  silver  nitrate,  the  picture  is  brought  out,  or  "  devel- 
oped "  as  the  process  is  technically  described. 

Fixing'.  —  The  next  step  is  to  dissolve  away  the  unde- 
composed  iodide,  in  order  to  make  the  picture  permanent ;  for 
it  is  evident  that  if  any  of  this  remains  in  the  film  the  light 
will  continue  to  work,  and  thus  destroy  the  picture.  This  is 
done  by  washing  the  plate  in  a  saturated  solution  of  sodium 
hyposulphite.  After  this  the  plate  is  thoroughly  washed  in 
water,  dried,  and  varnished  on  the  picture  side,  to  preserve 
the  film  from  injury. 

The  Lights  and  Shades  are  Inverted.  —  When  a  pho- 
tograph on  glass  is  viewed  by  transmitted  light,  it  will  be 
seen  that  the  shades  of  the  object  are  lights  on  the  picture, 
the  lights  and  shades  being  reversed.  Such  a  picture  is 
called  a  NEGATIVE.  If  the  "  development  "  be  pushed  far- 
ther, more  of  the  iodide  in  the  film  will  be  decomposed,  and 

IUITIVBRSITY! 


242  CHEMISTRY. 

the  shades  will  more  completely  intercept  the  light.  From 
such  a  negative  a  picture  may  be  printed  upon  paper.  This 
picture  of  the  negative  reverses  the  lights  and  shades  again, 
and  hence  brings  them  true  to  the  object.  Such  a  picture, 
in  which  the  lights  and  shades  are  the  same  as  those  of  the 
object  itself,  is  called  a  POSITIVE. 

261.  Making-  the  Positive.  —  The  paper  for  this  pur- 
pose is  prepared  by  floating  i£  first  upon  a  solution  of  salt, 
and  afterward  upon  one  of  silver  nitrate.  Silver  chloride 
(Ag  Cl)  is  thus  formed  in  the  paper.  This  paper,  placed 
under  the  negative,  is  exposed  to  light ;  the  light  is  stopped 
by  the  shades  of  the  negative,  but  passes  freely  through  its 
lights  :  upon  the  paper,  therefore,  the  lights  and  shades  cor- 
respond with  those  of  the  object  from  which  the  negative 
was  taken. 

The  photograph  is  next  to  be  thoroughly  washed  and  then 
"  toned."  The  toning-bath  is  a  solution  of  hydrosodium 
carbonate  (bicarbonate  of  soda),  containing  a  little  gold 
chloride  ( Au  C13) .  The  change  produced  by  this  bath  is 
beautiful  to  witness.  From  an  unpleasant,  dull,  reddish 
color,  the  picture  visibly  changes  to  a  rich  blue-black.  The 
picture,  having  next  been  washed  in  water  to  remove  all 
traces  of  the  gold  bath,  is  soaked  for  some  minutes  in  sodium 
hyposulphite,  to  wash  out  all  of  the  undecom posed  chloride, 
and  afterward  for  twenty-four  hours  in  water,  to  remove  all 
traces  of  the  hyposulphite. 


SECTION   XI. 

METALS  OF  THE  GOLD  CLASS. 

262.  General  Description.  —  The  metals  of  the  gold 
class  are  always  found  in  the  metallic  state.  They  are  not 
tarnished  by  air  at  any  temperature  short  of  their  melting- 
points,  nor  can  they  be  dissolved  by  nitric  acid.  Only 


CHEMISTRY.  243 

chlorine  or  aqua-regia  can  dissolve  them.     Gold  and  platinum 
are  the  most  familiar  and  important  members  of  the  class. 

263.  Gold.  —  In  small  quantities  gold  is  very  widely  dis- 
tributed in  nature.  Fine  grains  of  it  occur  in  the  sands  at 
the  bottom  of  many  rivers,  in  the  crystalline  rocks  and  the 
soils  derived  from  them.  Iron  pyrites,  found  almost  every- 
where, often  contains  traces  of  gold ;  and  silver  is  never 
found  entirely  free  from  it.  Few  places,  however,  seem  to 
possess  the  precious  metal  in  quantities  that  will  pay  for  the 
laborious  work  of  separating  it  from  the  sands  or  rocks  in 
which  it  is  found. 

Separation  of  Gold.  —  Except  osmium,  iridium,  and 
platinum,  gold  is  the  heaviest  of  metals.  It  is  very  much 
heavier  than  sand ;  so  that  when  gold-bearing  sand  is  vio- 
lently shaken  in  water,  the  fine  and  precious  grains  quickly 
sink  to  the  bottom,  while  the  sand  may  be  poured  off  with  the 
water.  By  repeating  this  process,  called  WASHING,  the  sand 
or  other  loose  material  is  finally  all  washed  away.  The 
fine  metallic  grains  left  behind  are  seldom  pure  gold.  The 
baser  metals  —  silver,  copper,  and  others  —  are  taken  out 
by  sulphuric  or  nitric  acid,  in  which  they  will  dissolve,  but 
which  can  not  dissolve  the  gold.  This  process  of  separating 
gold  from  the  metals  with  which  it  is  alloyed  is  called 
REFINING. 

When  the  native  gold  is  scattered  in  fine  grains  through 
solid  rock,  it  is  extracted  by  AMALGAMATION.  Mercury  mixed 
with  the  crushed  ore  d;  ssolves  the  gold  :  the  amalgam  is  then 
separated  from  the  excess  of  mercury  by  filtration,  and  the 
remainder  of  the  mercury  is  afterward  driven  away  com- 
pletely from  the  gold  by  distillation. 

Properties  of  Gold.  —  Gold  is  remarkable  for  its  fine 
yellow  color  and  beautiful  luster.  This  metal  is  about  nine- 
teen times  heavier  than  water ;  its  specific  gravity  is  19.33. 
It  is  the  most  malleable  of  metals  :  it  is  said  that  leaves  have 
been  beaten  so  thin  that  280.000  would  be  needed  to  ma_ 


244  CHEMISTRY. 

an  inch  in  thickness  !  There  is  a  curious  fact  about  the  color 
of  gold-leaf  ;  it  is  this  :  looked  at  in  the  usual  way  it  is  yel- 
low ;  but  let  a  leaf  be  spread  upon  glass  so  that  it  may  be 
viewed  in  transmitted  light,  and  it  exhibits  a  fine  green  color. 

264.  Platinum.  —  Platinum    is    a    rare    metal,    not    so 
widely  distributed  as  gold.     The  slopes  of  the  Ural  Moun- 
tains, Brazil,  and  Peru  are  among  the   localities  richest  in 
this  metal.     It  is  always  found  in  the  metallic  state,  but 
never  pure.     It  is  heavier  than  gold,  and  is  obtained  from 
loose  sands  or  soils  by  washing  in  the  same  way.     Its  com- 
mercial value  is  about  one-half  that  of  gold  and  about  eight 
times  that  of  silver. 

Pure  platinum  is  almost  as  white  as  silver,  and  can  not  be 
tarnished  in  air  at  any  temperature.  The  most  intense  heat 
of  the  blow-pipe  is  needed  to  melt  it.  On  these  accounts 
platinum  vessels  are  much  used  in  the  laboratory.  Few 
indeed  are  the  chemicals  which  can  affect  it.  Aqua-regia 
and  the  caustic  alkalies  are  among  those  which  can.  On  the 
other  hand,  it  readily  forms  alloys  with  most  other  metals ; 
and  these  are  more  easily  melted  than  the  metal  itself,  and 
are  soluble  in  acids. 

REVIEW. 
L  — SUMMARY   OF  PRINCIPLES. 

265.  Malleability,  ductility,  conductivity,  and  luster  are 
the  most  characteristic  properties  of  the  metals. 

They  occur  in  nature  in  the  form  of  ores,  in  which  they 
are  combined  with  non-metals  ;  as  alloys,  in  which  they  are 
combined  with  one  another ;  and  as  native  metals,  in  which 
condition  they  are  uncombined. 

The  art  of  extracting  metals  from  their  ores  is  called 
metallurgy. 

Roasting  and  reducing  are  two  important  operations  in 
metallurgy.  Roasting  consists  in  heating  the  ore  in  the 
presence  of  air  :  its  object  is  to  change  the  ore  to  an  oxide  of 


CHEMISTRY.  245 

the  metal.  Reducing  consists  in  heating  the  oxide  with  car- 
bon, or  some  other  reducing  agent :  its  object  is  to  decompose 
the  compound,  and  set  the  metal  free. 

The  metals  of  the  alkalies  are  lighter  than  water,  soft  as 
wax,  univalent,  and  have  so  strong  attraction  for  oxygen 
that  they  decompose  water  at  low  temperatures.  Potassium 
and  sodium  are  the  leading  members  of  the  group. 

Potassium  is  a  constituent  in  plants  ;  and  when  wood,  for 
example,  is  burned,  the  potassium  is  changed  into  potassium 
carbonate. 

The  carbonate  is  obtained  in  solution  from  the  wood-ashes 
by  treating  them  with  water.  This  lye  yields  the  solid  potash 
by  evaporation,  and  the  potash  becomes  pearlash  by  heat. 
A  solution  of  pearlash  yields  crystals  of  pure  potassium 
carbonate. 

Sodium  chloride  is  the  most  abundant  compound  of  sodium. 
It  is  largely  used  in  making  other  useful  compounds  of 
sodium. 

Treated  with  sulphuric  acid  this  salt  yields  sodium  sul- 
phate, or  Glauber's  salts. 

The  sodium  sulphate  is  reduced  by  carbon  to  sodium 
sulphide. 

Sodium  sulphide  is  changed  by  calcium  carbonate  into 
sodium  carbonate,  or  black  ash. 

Black  ash,  by  leaching  and  evaporation,  yields  the  sodium 
carbonate  (Na2  C  O3)  of  commerce.  The  manufacture  of 
sodium  carbonate  from  sodium  chloride  (NaCl)  is  an  impor- 
tant industry. 

Treated  with  carbon  dioxide,  sodium  carbonate  becomes 
hydrosodium  carbonate.  This  is  the  substance  known  as 
baking-soda. 

The  metals  of  the  alkaline  earths  are  bivalent,  with  strong 
attraction  for  oxygen.  They  oxidize  rapidly  on  exposure  to 
air,  and  decompose  water  at  ordinary  temperatures. 

Calcium  is  the  most  common  metal  of  this  class.  Its 
compounds  are  abundant  in  nature  and  useful  in  the  arts. 


246  CHEMISTRY. 

Aluminium  and  indium  are  called  the  "  metals  of  the 
earths." 

Aluminium  is  very  abundant  in  the  earth  :  it  is  a  constitu- 
ent of  all  clay  soil  and  rocks,  in  which  it  exists  chiefly  as  the 
silicate. 

The  metals  of  the  zinc  class  can  be  easily  melted  and 
vaporized,  and  burn  freely  when  heated  in  air.  They 
decompose  water  at  high  temperatures,  and  evolve  hydrogen 
from  dilute  acids. 

Zinc  is  the  leading  member  of  the  class.  It  is  a  bluish- 
white  metal,  malleable  at  temperatures  between  100°  and 
loO°  C.  and  not  easily  oxidized  by  exposure  to  air. 

The  metals  of  the  iron  class  melt  with  difficulty,  and  are 
not  volatilized  by  the  intense  heat  of  the  furnace.  Iron  is 
the  leading  member  of  the  class. 

In  commerce  iron  occurs  in  three  forms;  viz.,  cast-iron, 
wrought-iron,  and  steel. 

These  differ  in  the  quantity  of  carbon  in  combination  with 
iron. 

Iron  ore  is  reduced  in  the  blast-furnace,  which  yields  the 
metal  in  form  of  pig-iron. 

The  cast-iron  is  changed  to  wrought-iron  in  the  reverbera- 
tory  furnace  by  the  action  of  the  oxygen  of  the  air. 

Steel  is  made  by  burning  the  carbon  out  of  cast-iron  in 
the  Bessemer  process,  or  by  causing  carbon  to  combine  with 
wrought-iron  in  the  cementation  process. 

Of  the  tin  class,  tin  is  the  only  useful  metal. 

Tinstone,  which  is  an  oxide  of  the  metal,  is  the  only  ore 
from  which  tin  is  obtained. 

Tin  is  a  bluish-white,  malleable  metal,  not  easily  oxidized, 
retaining  its  luster  on  exposure  to  air. 

Common  •'  tin  "  is  sheet-iron  coated  with  a  film  of  tin, 

Of  the  metals  of  the  antimony  class,  antimony,  arsenic, 
and  bismuth  are  the  most  interesting.  These  metals  are 
closely  related  to  the  non-metals  of  the  trivalent  group. 

The  metals  of  the  lead  class  are  lead  and  thallium. 


CHEMISTRY.  247 

Lead  is  a  soft  metal,  11.2  times  heavier  than  water. 

The  principal  ore  of  lead  is  galena,  from  which  it  is 
obtained  by  heating  with  lime  in  a  reverberatory  furnace. 

The  compounds  of  lead  are  poisonous,  and  hence  the  risk 
which  attends  the  use  of  lead  for  cisterns. 

The  metals  of  the  silver  class,  copper,  mercury  and 
silver,  are  often  found  native.  Their  sulphides  are  their 
most  abundant  ores. 

Copper  is  a  red  metal,  very  tenacious,  and  very  ductile. 
It  is  an  excellent  conductor  of  electricity.  Its  surface  is 
tarnished  by  exposure  to  air,  and  it  is  readily  attacked  by 
acids. 

Mercury  is  a  liquid  metal,  13.5  times  heavier  than  air.  It 
does  not  combine  with  oxygen  on  exposure  to  air.  It  forms 
two  oxides  and  two  chlorides.  Calomel  is  the  mercurous 
chloride,  and  corrosive  sublimate  is  the  mercuric  chloride. 

Alloys  of  mercury  are  called  amalgams. 

Silver  is  a  white  metal,  very  malleable  and  ductile,  not 
affected  by  air  or  oxygen,  but  blackened  quickly  by  sulphuret- 
ted hydrogen. 

Silver  is  obtained  from  argentiferous  galena  by  cupel- 
lation.  It  is  obtained  from  other  ores  by  first  changing  them 
to  oxides,  then  reducing  the  oxides  by  iron,  and  finally  sep- 
arating the  silver  by  amalgamation. 

Silver  coin  of  the  United  States  is  an  alloy  with  copper, 
containing  ninety  per  cent  of  silver. 

The  metals  of  the  gold  class  are  always  found  native. 
They  are  not  affected  by  oxygen,  and  can  not  be  dissolved 
in  strong  acids.  They  have  a  strong  attraction  for  chlorine, 
and  dissolve  in  aqua-regia. 

Gold  is  a  soft  and  heavy  metal,  yellow  by  reflected  light, 
and  green  by  transmitted  light.  It  is  malleable  in  the 
highest  degree. 

Platinum  is  almost  as  white  as  silver,  not  affected  by 
oxygen,  but  soluble  in  aqua-regia. 


248  CHEMISTEY. 


II. —EXERCISES. 

Name  the  characteristic  properties  of  metals.  What  of 
their  melting  ?  Of  their  weight  ?  In  what  condition  are  they 
found  in  nature  ? 

Into  how  many  classes  are  they  grouped  ? 

Describe  the  metals  of  the  first  class. 

Illustrate  the  class  properties.  How  does  potassium  act 
upon  ice?  Give  the  reaction.  What  difference  between 
alkalies  and  other  hydrates  ? 

Describe  the  manufacture  of  pearlash.  Of  pure  potassium 
carbonate. 

Describe  the  manufacture  of  potassium  hydrate.  What 
are  its  properties  ? 

What  is  the  composition  of  sodium  chloride  ?  How  is  it 
obtained  ?  For  what  is  it  used  ? 

Show  how  sodium  chloride  is  changed  to  sodium  sulphate. 
What  are  Glauber's  salts? 

Show  how  sodium  sulphate  is  changed  to  sodium  sulphide. 

Show  how  sodium  sulphide  is  changed  to  sodium  carbonate. 
What  is  the  final  process  in  this  manufacture  ? 

Give  a  brief  description  of  hydrosodium  carbonate. 

Give  a  brief  description  of  the  metals  of  the  alkaline 
earths. 

Illustrate  the  bivalent  character  of  calcium. 

What  is  slaked  lime  ?  For  what  is  it  used  ?  How  is  mortar 
made?  What  class  of  salts  do  the  members  of  this  group 
form?  Are  they  soluble  in  water?  How  are  bicarbonates 
formed?  Explain  the  production  of  stalactites. 

What  is  said  of  the  metals  of  the  earths? 

Describe  aluminium. 

What  is  said  of  the  metals  of  the  zinc  class? 

How  is  zinc  obtained  ?     What  are  its  properties  ? 

Illustrate  the  class  properties,  as  to  melting-point ;  as  to 
vaporization  ;  as  to  combustion  ;  as  to  their  action  on  water. 

What  is  said  of  the  metals  of  the  iron  class  ? 


CHEMISTRY.  249 

In  what  ores  chiefly  is  iron  found?  Name  its  three  com- 
mercial forms. 

What  is  cast-iron  ?     How  obtained  ? 

Describe  the  blast-furnace. 

Describe  in  full  the  process  of  getting  cast-iron  from  its 
ores. 

What  is  wrought- iron  ?     How  obtained  ? 

Describe  the  reverberatory  furnace. 

Describe  in  full  the  process  of  making  wrought-iron. 

What  is  steel  ?     How  made  ? 

Describe  the  "  Bessemer  process." 

Describe  the  process  of  cementation. 

What  is  said  of  the  metals  of  the  tin  class  ? 

How  is  tin  obtained  ?  What  are  some  of  its  properties  ? 
For  what  is  it  used  ? 

What  is  said  of  the  metals  of  the  antimony  class  ? 

What  is  said  of  arsenic? 

Describe  antimony. 

What  is  type-metal  ? 

Describe  bismuth. 

What  is  said  of  its  alloys  ? 

What  is  said  of  the  metals  of  the  lead  class  ? 

What  of  the  properties  of  lead  and  thallium  ? 

From  what  ore  is  lead  obtained?     Describe  the  process. 

What  are  the  uses  of  lead?  What  is  said  of  its  use  for 
water-pipes  ? 

What  is  said  of  the  metals  of  the  silver  class  ? 

How  does  copper  occur  in  nature  ? 

Describe  the  smelting  of  copper  ores.  Also,  the  process 
of  refining. 

What  are  the  properties  of  copper? 

Describe  its  alloys,  —  brass,  bronze,  gun-metal,  German 
silver. 

In  what  condition  is  mercury  found  ?  What  is  a  peculiar 
property  of  this  metal  ?  What  are  its  uses  ?  What  is  calo- 
mel ?  What  is  corrosive  sublimate  ?  What  are  amalgams  ? 


250  CHEMISTRY. 

In  what  condition  is  silver  found  in  nature  ?  Name  some 
important  localities. 

By  what  process  is  silver  obtained  from  galena  rich  in 
silver  ?  With  poor  galena,  what  process  is  first  used  ?  Upon 
what  principle  is  cupellation  based?  Describe  the  process. 

With  what  ores  is  amalgamation  used  to  obtain  the  silver? 
What  preliminary  treatment  needed  ?  Describe  the  process 
of  amalgamation. 

What  is  said  of  the  alloys  of  silver? 

What  art  depends  upon  the  chemical  action  of  light? 

What  are  photographs  ? 

How  is  collodion  made?  How  is  a  plate  of  glass  coated 
with  it  ?  What  is  the  effect  of  light  upon  the  coated  plate  ? 
How  is  the  picture  developed?  Describe  the  rest  of  the 
process. 

What  is  a  "  negative  "  ?  How  is  the  paper  prepared,  and 
the  ' '  positive  ' '  made  ?  What  other  processes  are  gone 
through  with  to  finish  the  picture  ? 

What  is  said  of  the  gold  class  ? 

Where  is  gold  found,  and  in  what  condition  ?  How  is  it 
separated  from  sand  ?  From  baser  metals  ?  From  rocks  in 
which  fine  grains  are  scattered? 

How  does  platinum  occur  in  nature  ?  How  is  it  obtained  ? 
What  are  some  of  its  properties  ? 


APPENDIX. 


EASY   EXPERIMENTS   FOR   THE   CLASS-ROOM. 

IT  is  recommended  that  the  following  experiments  be  made, 
in  addition  to  those  described  in  the  text.  The  numbers  in 
heavy  type  refer  to  the  paragraphs  of  the  book  which  the 
experiments  more  fully  illustrate  or  extend. 

No  attempt  is  here  made  to  furnish  a  manual  of  chemical 
manipulation.  Remembering  the  conditions  which  surround 
the  teachers  of  chemistry  in  a  majority  of  our  schools,  it  is 
believed  that  no  genuine  service  would  be  done  by  calling 
their  attention  to  costly  apparatus,  lengthy  or  delicate  pro- 
cesses, or  even  to  a  large  number  of  experiments.  In  the 
selections  which  follow,  the  teacher  will  find  those  which  he 
can  use,  and  which  he  can  use  with  the  smallest  expenditure 
of  money,  time,  and  patience,  because  they  combine  in  the 
highest  degree,  — 

Simplicity  of  details, 
Certainty  of  results, 
Cheapness  of  materials, 
Adaptation  to  the  subject. 

1.  Physical  Changes.  —  Ex.  1.  Provide  a  Bunsen's 
burner,  a  piece  of  platinum  wire  about  two  inches  long,  a 
piece  of  magnesium  wire  or  ribbon  about  six  inches  long, 
and  a  pair  of  forceps. 

251 


252  CHEMISTRY. 

With  the  forceps,  hold  the  platinum  wire  in  the  flame  of 
the  lamp,  and  notice  that  it  glows  with  a  bright  red  heat,  but 
that  it  suffers  no  change  in  its  nature. 

With  the  forceps,  then  hold  the  magnesium  with  one  end  in 
the  flame,  and  notice  that  it  glows  with  a  red  heat,  then  takes 
fire,  and  burns  with  vivid  brightness,  and  that  it  is  at  the 
same  time  changed  into  an  entirely  different  kind  of  matter. 

3.  Chemical  Change.  —  Ex.  2.  Provide  a  test-tube,  a 
saturated  solution  of  calcium  chloride,  and  some  dilute  sul- 
phuric acid  (1  of  acid  to  4  of  water).  Fill  the  tube  to  the 
height  of  two  inches  with  the  calcium  chloride,  and  then 
add,  all  at  once,  the  dilute  acid  two  inches  more,  and  shake 
quickly,  or  stir  with  a  glass  rod.  These  colorless  liquids 
combine,  and  produce  a  white  solid,  which  will  not  fall  out  of 
the  tube,  even  when  held  bottom  upward. 

Ex.  3.  Fill  a  cylinder  two- thirds  full  of  water,  and  add 
about  fifty  cubic  centimeters  of  a  solution  of  lead  acetate. 
Then  add,  little  by  little,  some  potassium  chromate.  These 
colorless  liquids  yield  a  rich  ydlow  solid. 

10.  Mechanical  and  Chemical  Attractions.  —  Ex.  4. 

Take  two  pieces  of  plate-glass,  very  clean  and  smooth,  and 
slide  one  upon  the  other,  gently  pressing  them  together  at 
the  same  time.  Notice  that  they  cling  firmly.  The  lower 
one  may  be  lifted  by  the  upper.  They  are  held  together  by 
cohesion,  or,  as  we  are  accustomed  to  say,  by  adhesion. 
Cohesion  is  the  generic  name  given  to  all  attraction  among 
molecules. 

Ex.  5.  Use  a  magnet  with  small  nails,  and  notice  the  effect 
of  magnetic  attraction. 

No  permanent  effect  is  left  on  bodies  by  the  action  of  these 
attractions. 

Ex.  6.  Take  two  wide-mouthed  bottles  of  equal  size. 
Moisten  the  inside  of  one  with  ammonia,  and  the  inside  of 
the  other  with  hydrochloric  acid.  Invert  one,  and  stand  it 
upon  the  other,  mouth  to  mouth.  Notice  that,  whereas  the 


APPENDIX.  253 

contents  of  both  were  colorless,  both  are  now  filled  with 
white  fumes.  Two  colorless  gases,  ammonia  and  hydro- 
chloric acid,  have  united  to  form  a  white  solid.  They  are 
held  in  combination  by  chemical  attraction. 

11.  Influence  of  Cohesion.  — Ex.  7.  Mix  a  little  coarsely 
powdered  copper  sulphate  with  an  equal  quantity  of  coarsely 
powdered  potassium  ferrocyanide  in  a  mortar,  and  notice 
that  no  chemical  change  occurs.  Grind  them  together  :  still 
no  chemical  change.  Sprinkle  a  little  of  the  fine  powder 
into  a  cylinder  of  water,  and  notice  the  dark  red- brown  solid 
produced. 

Ex.  8.  Mix  a  little  ferrous  sulphate,  in  powder,  with  a 
little  powdered  potassium  ferrocyanide  :  no  chemical  action 
occurs.  Sprinkle  a  very  little  of  the  mixed  powder  upon 
water  in  a  cylinder,  and  notice  the  fine  blue  compound 
produced. 

14.  Influence  of  Light.  —  Ex.  9.  Into  a  cylinder  of 
water  put  a  small  quantity  of  silver  nitrate,  and  then  add  a 
little  hydrochloric  acid.  Observe  the  dense  milk-white  pre- 
cipitate which  forms.  Place  the  cylinder  in  the  strong  sun- 
light, and  notice  the  change  from  white  to  a  purplish-black. 

17.  No  Loss  nor  Gain.  —  Ex.  10.  Provide  two  beakers. 
Into  one  put  about  a  hundred  cubic  centimeters  of  moderately 
strong  solution  of  lead  nitrate,  and  into  the  other  put  half  as 
much  solution  of  potassium  chromate.  Then  put  the  two 
upon  one  pan  of  the  balance,  and  weigh  them  carefully. 
Next,  pour  the  chromate  into  the  nitrate,  and  restore  the 
beaker  to  its  place.  The  weight  will  be  found  unchanged, 
notwithstanding  the  production  of  a  very  abundant  yellow 
solid. 

24.  The  Law  of  Constant  Proportions.  —  Ex.  11.  Fill 
a  test-tube  about  one-third  full  of  water,  and  add  about  a 
quarter  of  an  inch  of  silver  nitrate  solution.  To  this  add  a 
few  drops  of  hydrochloric  acid,  and  shake  it  vigorously.  The 


254  CHEMISTRY. 

precipitate  will  soon  settle.  To  the  clear  liquid  above  the 
precipitate,  again  add  drops  of  the  acid,  and  repeat  the  opera- 
tion until  the  last  drops  added  give  no  precipitate  at  all. 
The  nitrate  is  then  all  used  up  by  the  acid  to  make  the 
white  chloride. 

Then  add  drops-  of  the  nitrate :  a  white  precipitate  shows 
that  the  acid  had  been  added  in  excess  of  what  was  needed. 
Add  nitrate  as  long  as  a  precipitate  is  formed :  it  will  require 
but  few  drops. 

The  slightest  quantity  of  either,  beyond  a  certain  definite 
proportion,  remains  unchanged. 

Ex.  12.  Into  a  small  beaker  pour  about  fifty  cubic  centi- 
meters of  hydrochloric  acid,  and  drop  into  it,  little  by  little, 
powdered  sodium  carbonate  until  the  last  small  quantity  pro- 
duces no  effervescence.  The  acid  is  then  all  neutralized. 
Then  stir  in  drops  of  the  acid  patiently  until  with  the  last 
drop  the  last  of  the  small  quantity  of  solid  carbonate  dis- 
appears. 

Each  of  these  substances  requires  a  certain  definite  pro- 
portion of  the  other :  any  excess  remains  unchanged. 

Ex.  13.  Evaporate  the  clear  liquid  obtained  in  the  fore- 
going experiment,  and  you  will  get  a  good  sample  of  com- 
mon salt  which  was  produced  in  the  chemical  action. 

30.  The  Molecule.  —  Ex.  14.  Dissolve  a  piece  of  ani- 
line-red, no  larger  than  the  head  of  a  small  pin,  in  a  thim- 
ble-full of  alcohol,  and  then  pour  the  solution  into  a  half- 
gallon  jar  of  clear  water.  Notice  the  crimson  color  imparted 
to  the  whole.  Let  us  estimate  the  half -gallon  to  contain 
30,000  drops  of  water,  and  that  to  color  a  single  drop  so  uni- 
formly must  require  one  hundred  of  the  minute  pieces  into 
which  the  aniline-red  is  divided,  and  we  must  then  infer  that 
the  small  piece  of  the  coloring  matter  has  been  broken  into 
no  less  than  three  millions  of  pieces.  Such  an  experiment 
illustrates  the  exceeding  great  divisibility  of  matter. 

Ex.   15.     Fill  a  cup  to  the  brim  with  hot  water :  sprinkle 


APPENDIX.  255 

into  it  slowly  some  finely  ground  loaf-sugar.  Notice  that 
the  sugar  disappears,  and  further  that  the  cup  is  no  fuller 
than  before.  Two  or  three  tea-spoonfuls  of  sugar  may  be 
added  before  the  water  overflows. 

Ex.  1C.  Take  a  cylinder,  and  fill  it  with  alcohol  to  a 
height  carefully  marked  with  a  rubber  ring,  or  even  a  thread 
tied  around  it.  Take  cotton,  and  pick  it  out  into  fine  shreds, 
and  then  introduce  it,  little  by  little,  into  the  alcohol,  care- 
fully pressing  it  down  to  the  bottom  with  a  glass  rod.  A 
large  quantity  of  cotton  may  be  introduced  without  raising 
the  level  of  the  liquid. 

These  two  experiments  can  be  explained  only  by  supposing 
that  the  minute  parts  of  the  water  or  the  alcohol  are  not  in 
actual  contact,  and  that  the  minute  parts  of  the  sugar  or 
cotton  enter  into  the  spaces  between  them.  ' 

Such  experiments  as  these  fall  far  short  of  giving  a 
demonstration  of  the  existence  of  molecules  :  nevertheless 
they  are  useful,  since  they  pave  the  way  to  a  clearer  concep- 
tion of  the  molecule  and  of  molecular  spaces. 

35-41.  Chemical  Nomenclature. — A  useful  exercise  to 
precede  the  study  of  the  nomenclature  may  be  conducted  as 
follows  :  — 

Ex.  17.  Place  upon  the  table,  in  a  promiscuous  group, 
bottles  containing  acids,  bases,  and  neutral  substances,  two, 
three,  or  more  of  each.  Provide  also  two  cylinders,  a  solu- 
tion of  blue  litmus,  and  a  pitcher  of  water. 

Nearly  fill  the  cylinders  with  water,  and  add  litmus  enough 
to  give  a  distinct  blue  color  to  both. 

Then  proceed  to  test  the  effect  of  each  one  of  the  sub- 
stances by  adding  a  few  drops  to  the  litmus.  Those  which 
redden  the  blue  color,  place  together  in  a  group  at  one  side ; 
those  which  restore  the  blue  color  of  reddened  litmus,  place 
in  a  group  at  the  other  side  ;  and  those  which  have  no  effect 
upon  either  the  blue  or  the  red  litmus,  place  together  in  a 
third  group. 


256  CHEMISTEY. 

The  classification  of  substances  as  acids,  bases,  and 
neutral  bodies,  is,  in  this  way,  clearly  illustrated. 

If  you  have  selected  binary  compounds,  as,  for  example, 
water,  potassium  iodide,  mercuric  chloride,  to  represent 
neutral  bodies,  you  can  easily  make  these  an  introduction  to 
the  study  of  paragraph  36,  by  writing  their  formulas  on  the 
blackboard,  to  show  the  meaning  of  the  term  binary. 

They  will  be  useful  again,  when  you  reach  the  topic  "  Other 
Binary  Compounds,"  to  illustrate  the  nomenclature. 

39.  Salts.  —  Ex.  18.  Into  a  beaker  put  some  dilute  sul- 
phuric acid,  and  drop  into  this  some  fragments  of  zinc. 
Violent  effervescence  soon  begins,  atoms  of  zinc  taking  the 
place  of  atoms  of  hydrogen ;  and  this  may  be  kept  up  by 
adding  fresh  pieces  of  the  metal  until  the  acid  is  exhausted. 

Ex.  19.  Filter  the  fluid  just  obtained,  while  hot,  and  then 
allow  it  to  stand  quietly  until  cold.  A  mass  of  the  white 
crystalline  salt,  zinc  sulphate,  will  be  obtained. 

Ex.  20.  Repeat  the  experiments,  using  iron  in  the  form 
of  small  nails  instead  of  zinc,  and  the  green  crystalline  salt, 
ferrous  sulphate,  will  be  produced. 

Ex.  21.  A  small  piece  of  sodium  may  be  dropped  upon 
the  surface  of  dilute  sulphuric  acid.  The  salt  hydro-sodium 
sulphate  will  be  formed. 

36-41.  A  very  useful  exercise  to  follow  the  study  of  the 
nomenclature  may  be  conducted  as  follows :  Place  upon  the 
table  bottles  containing  substances  representing  all  classes 
whose  names  have  been  studied.  Their  labels  should  contain 
their  names  only.  Let  a  student  be  given  a  bottle,  and  let 
him,  after  reading  the  name  of  the  substance  in  it,  be  asked 
to  state,  to  what  class  of  compounds  it  belongs.  If  a  binary, 
then  what  are  its  constituents,  and  in  what  proportions,  and 
what  is  its  formula  ? 

If  an  acid,  then  of  which  class,  and  what  are  its  constit- 
uents ? 

If  a  base,  then  what  are  its  constituents? 


APPENDIX.  257 

If  a  salt,  then  from  what  acid  may  we  consider  it  to  be 
derived  ?     By  what  substitution  ?     What  are  its  constituents  ? 

50.  Hydrogen.  —  In   experimenting  with   hydrogen   the 
greatest  care  should  be  taken  to  have  the  gas  unmixed  with 
air,   otherwise   unexpected    explosions   may   occur.     Before 
collecting  the  gas  in  receivers,  all  air  should  be  driven  out  of* 
the  apparatus.     To  know  whether  the  gas  is  coming  off  free 
from  air,  it  may  be  tested  by  collecting  a  test-tube  full,  and, 
keeping  its  mouth  downward,  apply  the  flame  of  a  match. 
If  the  gas  continues  to  burn  quietly  after  the  first  slight 
explosion,  it  is  pure  enough.     If  the  explosion  is  sharper, 
and  no  flame  at  all  survives  it,  the  gas  is  dangerous. 

51.  Reaction  with  Iron.  —  Ex.  22.     Put  a   few  small 
nails  into  a  test-glass,  and  cover  them  with  dilute  sulphuric 
acid,  made  by  mixing  one  part  of  the  acid  with  three  parts 
of  water.     Cover   the    glass  with   a   glass  plate.     Light   a 
match  after  the  effervescence  has  gone  on  rapidly  half  a 
minute,  and,  removing  the  glass  cover,  bring  the  flame  to 
the  mouth  of  the  glass.     Notice  the  slight  explosion  which 
follows.     Perhaps  the  flame  will  continue  to  play  above  the 
foaming  liquid  in  the  glass.     Hydrogen  is  evolved  by  the 
chemical  action  as  follows  :  — 

Fe"  +  H2  S  O4  =  Fe  S  O4  +  H2. 

The  bivalent  atom  of  iron  takes  the  place  of  two  atoms  of 
hydrogen  in  the  molecule  of  acid. 

52.  Lightness  of  Hydrogen.  —  Ex.  23.     Fill  a  small  jar 
with  hydrogen.     Lift  it  from  the  cistern  of  water,  and  turn 
its  mouth  upward.     Carry  it  two  or  three  paces  away,  and 
then  bring  a  lighted  taper  into  the  jar :  no  hydrogen  will  be 
detected.     Its  quick  escape  from  the   jar  shows   it   to   be 
lighter  than  air. 

Ex.  24.     Lift   another    jar   full   of    hydrogen   from   the 
cistern,  and  keep  its  mouth  downward  while  it  is  carried 


258  CHEMISTRY. 

away  in  the  same  manner.  Bring  a  lighted  taper  to  its 
mouth :  the  hydrogen  takes  fire,  showing  that  the  gas  has 
remained  in  this  inverted  jar,  proving  again  that  it  is  lighter 
than  air. 

Ex.  25.  Hydrogen  Soap-Bubbles. —  Remove  the  deliv- 
ery tube  of  the  hydrogen-generator  (Fig.  23)  from  the  cistern, 
and  attach  it  to  the  stem  of  a  tobacco-pipe  by  rubber  tubing. 
Having  the  soap  solution  in  a  capsule,  dip  the  bowl  of  the 
pipe  into  it  in  the  usual  way,  and  let  the  gas,  as  it  comes 
over  from  the  bottle,  blow  the  bubble.  While  the  bubble  is 
still* small,  turn  the  mouth  of  the  pipe  upward.  The  bubble, 
having  attained  a  diameter  of  three  or  four  inches,  will 
break  away,  or  else  it  may  be  easily  detached  by  a  sudden 
movement  of  the  pipe  downward.  It  will  then  rise  rapidly. 

53.  Explosive  Bubbles.  —  Ex.  26.  Cover  the  bottom  of 
a  dinner-plate  with  the  bubble  solution.  Place  the  mouth 
of  the  pipe  in  the  solution,  slowly  moving  it  from  place  to 
place,  until  a  number  of  small  bubbles  rest  upon  the  surface. 
Remove  the  pipe,  and  shortly  afterward  toucli  the  bubbles 
with  the  flame  of  a  match,  which  for  this  purpose  may  be 
tied  upon  the  end  of  a  long  wire  handle. 

Air  passes  through  the  thin  film,  and  mixes  with  the  gas  to 
form  the  explosive  mixture. 

Ex.  27.  The  explosive  character  of  such  a  mixture  may 
also  be  shown  as  follows  :  — 

Into  a  wide-mouthed  bottle  put  some  fragments  of  zinc,  and 
just  cover  them  with  water.  Select  a  thin  cork,  which  fits 
the  bottle  not  too  tightly,  and  make  a  hole  through  it  large 
enough  to  admit  a  match  easily.  Take  a  long  wire,  and  bend 
it  near  one  end  at  right  angles  to  itself.  Bind  a  match  upon 
this  short  bend  of  the  wire.  All  this  having  been  arranged, 
pour  enough  sulphuric  acid  into  the  bottle  to  liberate  hydro- 
gen with  some  rapidity.  Insert  the  perforated  cork,  and  wait 
about  half  a  miuute.  Then  fire  the  match,  and  by  means  of 
its  wire  handle  insert  its  flame  into  the  perforation  of  the 


APPENDIX.  259 

cork.     A  violent  but  harmless  explosion   instantly  follows, 
ejecting  the  cork  from  the  bottle. 

Ex.  28.  Put  a  quantity  of  the  soap-bubble  solution  into 
the  hand,  held  slightly  cup-shaped  to  retain  it.  Let  the  gas 
from  the  hydrogen  bottle  blow  a  bubble  on  this  solution,  as 
it  did  on  the  solution  in  the  plate,  Ex.  26.  Remove  the  pipe, 
and  touch  the  bubble  with  a  match  or  taper  flame,  held  in 
readiness  by  an  assistant.  An  explosion  follows,  while  the 
hand  on  which  it  occurs  scarcely  feels  the  slightest  jar. 
When  occurring  in  open  air  the  explosion  expends  its 
violence  in  sound ;  when  confined,  the  exploding  mixture 
shatters  the  vessel  which  holds  it,  as  would  a  charge  of 
gunpowder. 

57.  Chlorine.  —  Chlorine  is  such  a  peculiarly  suffocating 
gas,  that  great  care  should  be  taken  to  prevent  its  escape  into 
the  room.     All  joints  in  the  apparatus  should  be  perfectly 
air-tight.     The  receivers  should  not  be  filled  quite  to  the 
brim  with  the  gas.     In  changing  the  delivery- tube  from  one 
vessel  to  another,  the  transfer  should  be  made  as  quickly 
as  possible.     The  vessels  of  gas  should  be  kept  covered. 
Bottles   of   white   glass    are   very  good    chlorine   receivers, 
because  they  can  be  tightly  closed  with  a  cork  until  the  gas 
is  to  be  used. 

If  a  little  strong  sulphuric  acid  is  put  into  the  bottle,  so 
that  the  gas  must  bubble  through  it,  the  chlorine  will  be 
dried  thereby:  this  is  a  point  of  importance  in  some 
experiments. 

Ex.  29.  Chlorine  may  be  easily  prepared,  and  in  suffi- 
cient purity  for  some  purposes,  by  covering  the  bottom  of  a 
jar  or  bottle  with  bleaching-powder,  and  adding  a  little 
sulphuric  acid. 

58.  Solubility  of  Chlorine.  —  Ex.  30.     Provide  a  bot- 
tle with   a  perforated   cork,  through  which  passes    a   short 
piece  of  glass  tube,  or  even  a  piece  of  pipe-stem.     Fill  the 
bottle  about  one-third  full  of  water,  and  the  remaining  two- 


260  CHEMISTRY. 

thirds  with  chlorine  from  the  apparatus  in  Fig.  29.  Close 
the  bottle  with  its  cork  tightly.  Cover  the  end  of  the  tube 
with  the  finger  closely,  then  shake  the  whole  violently  for  a 
few  moments,  and  afterwards  insert  the  tube  in  a  vessel  of 
water,  and  remove  the  finger.  Water  will  be  seen  to  rise  into 
the  bottle  to  supply  the  place  of  the  gas  which  has  been 
dissolved. 

59.  Chemical  Properties.  —  Ex.  31.  Tie  a  small  tuft 
of  cotton  on  the  end  of  a  wire,  and  wet  it  with  ether.  Set  it 
on  fire,  and  lower  it  into  a  jar  of  chlorine.  The  combustion 
will  continue,  with  much  smoke. 

The  chlorine  combines  with  the  hydrogen  of  the  ether, 
but  not  with  its  carbon,  which  is  therefore  set  free. 

Ex.  32.  Bleaching.  —  Into  a  bottle  of  chlorine  pour  a 
little  litmus  solution  :  cork  the  bottle,  and  shake  it ;  the  color 
of  the  litmus  is  discharged. 

Ex.  33.  Black,  or  other  colored  ink,  may  be  used  instead 
of  litmus  solution. 

Ex.  34.  Moisten  a  piece  of  paper  containing  ordinary 
writing,  such  as  a  part  of  a  letter,  and  hang  it  awhile  in  a 
jar  of  chlorine.  The  writing  will  disappear. 

Ex.  35.  Try  the  experiment  with  a  piece  of  newspaper 
or  other  printed  paper.  Notice  that  the  characters  are  not 
destroyed.  The  coloring  matter  of  printer' s-ink  is  carbon, 
for  which  chlorine  has  little  attraction. 

Ex.  36.  Insert  a  rose,  or  other  colored  blossom,  in  a  jar 
of  moist  chlorine  :  it  will  be  speedily  bleached. 

62.  Iodine. — Ex.  37.  Put  a  few  crystals  of  iodine  into 
$,  clean  and  dry  flask,  and  gently  heat  it :  notice  the  fine  violet 
vapor. 

Ex.  38.  Solubility  of  Iodine.  —  When  the  flask  is 
sufficiently  cool,  pour  water  in,  to  fill  it  two- thirds  full. 
Shake  it  vigorously,  and  notice  the  brownish-yellow  color 
imparted  to  the  water.  Iodine  is  very  slightly  soluble  in 
water ;  1  part  of  iodine  requires  7,000  parts  of  water. 


APPENDIX.  261 

Ex.  39.  Pour  off  this  solution  ( iodine- water) ,  and  put 
a  little  alcohol  into  the  flask.  Notice  the  deep  reddish- 
brown  color  which  the  liquid  quickly  assumes.  Iodine  is 
very  soluble  in  alcohol.  A  solution  of  iodine  in  alcohol  is 
called  "tincture  of  iodine."  It  is  used  for  medicinal  pur- 
poses. 

Ex.  40.  Test  for  Iodine.  —  Boil  a  little  starch  in  a 
beaker  of  water,  and  pour  some  of  the  liquid  into  a  jar  of 
water.  Then  add  a  few  drops  of  ' '  iodine-water, ' '  and  notice 
the  fine  deep-blue  color  produced.  This  result  is  a  very 
delicate  test  for  the  presence  of  free  iodine. 

71.  Oxygen.  —  Certain  precautions  should  be  observed 
in  preparing  oxygen  (Fig.  36).  The  materials  should  be 
dry  and  well  powdered.  The  heat  should  be  applied  gently 
at  first,  and  afterward  so  regulated  that  a  steady  and  not  too 
rapid  stream  of  gas  will  be  evolved.  It  will  often  be  neces- 
sary to  withdraw  the  flame  altogether,  and  restore  it  again 
when  the  stream  of  gas  slackens. 

The  end  of  the  delivery-tube  must  be  taken  out  of  the 
water  before  the  gas  wholly  ceases  to  issue,  else,  as  the  flask 
cools,  atmospheric  pressure  forces  water  over  into  the  hot 
flask,  which  may  be  then  blown  to  pieces  by  the  sudden  evo- 
lution of  steam  within. 

The  quantity  of  material  needed  may  be  estimated  by 
remembering  that  about  two  gallons  of  gas  will  be  obtained 
from  an  ounce  of  potassium  chlorate. 

When  large  quantities  of  oxygen  are  desired,  metallic  flasks 
must  be  used  instead  of  glass  flasks,  which  are  too  frail. 

Ex.  41.  Fold  a  piece  of  tough  paper  into  a  narrow  band. 
Bend  this  band  around  the  upper  part  of  a  hard  glass  test- 
tube,  and  grasp  both  branches  of  it  between  the  thumb  and 
finger.  The  tube  is  thus  provided  with  a  convenient  handle. 

Put  about  a  quarter  of  an  inch  of  finely  powdered  potas- 
sium chlorate  into  the  tube,  and  apply  heat.  The  chlorate 
will  first  melt,  and  afterward  appear  to  boil.  Then  insert  a 


262  CHEMISTRY. 

lighted  match  into  the  mouth  of  the  tube,  and  notice  that  the 
vigor  of  its  combustion  is  increased.  Let  the  charred  end  of 
the  match,  with  a  spark  upon  it,  fall  upon  the  fused  mass  at 
the  bottom,  and  notice  the  brilliant  deflagration  which  fol- 
lows. The  chlorate  is  decomposed  by  heat,  yielding  oxygen. 

72.  Ex.    42.       Oxygen    heavier    than   Air.  —  Having 
two  small  jars  of  oxygen,  stand  one  of  them  with  its  open 
mouth  upward,  and  leave  it  uncovered  ;  and  the  other  with  its 
open  mouth  downward,  and  with  its  edges  resting  on  blocks  to 
support  it  above  the  table.     Then  test  the  jars  by  bringing  a 
lighted  taper  into  each.     It  will  be  found  that  the  taper  burns 
more    brilliantly    in   that   which    has    been   standing   mouth 
upward,  but  is  not   affected   by  the   other.     Evidently   the 
oxygen  has    fallen    out   of  the   latter.     Both   jars,  equally, 
show  that  this  gas  is  heavier  than  air. 

73.  Brilliant   Combustion.  —  Ex.  43.      Take    a   piece 
of  crayon,  and  provide  for  it  a  long  wire  handle,  so  that  it 
may  be  lowered  into  a  jar  of  gas.     This  may  be  done  by 
winding  one  end   of  the  wire   two   or  three   times   spirally 
around  the  crayon.     Scoop  out  the  upper  end  of  the  crayon, 
making  a  little  cup.     Into  this  cup  put  a  piece  of  camphor. 
Set  fire  to  the   camphor,  and  quickly  lower  it  into  a  jar  of 
oxygen :  it  will  burn  with  intense  white  light. 

Ex.  44.  Combustion  of  Zinc.  —  Cut  a  long  and  narrow 
strip  from  a  sheet  of  zinc,  and  coil  it  by  wrapping  it  spirally 
around  a  lead-pencil.  Remove  the  pencil,  and  wind  one  end 
of  the  strip  of  zinc  with  thread,  and  immerse  this  in  melted 
sulphur.  Next  set  fire  to  this  sulphur,  and  thrust  it  down 
into  a  jar  of  oxygen.  The  burning  sulphur  will  heat  the 
zinc,  which  will  quickly  take  fire,  and  burn  brilliantly. 

75.  Ozone.  —  To  prepare  the  test-paper  for  ozone,  take 
two  hundred  cubic  centimeters  of  water,  and  add  one  gram 
of  potassium  iodide.  When  solution  is  complete,  add  ten 
grams  of  finely  powdered  starch,  and  heat  gently  until  the 


APPENDIX.  263 

fluid  is  thickened  by  the  starch.  Let  narrow  strips  of  paper 
be  drawn  through  this  mixture.  The  paper  may  be  dried,  and 
kept  for  a  long  time  in  closely  stoppered  bottles  ;  but  it  must 
be  moistened  when  used. 

Heat  the  glass  rod  quite  too  hot  to  be  handled. 

When  phosphorus  is  used,  for  the  preparation  of  ozone,  let 
the  stick  be  first  held  under  water  while  its  surface  is  gently 
scraped  :  this  cleaning  of  its  surface  is  necessary  if  the  phos- 
phorus has  been  long  exposed  to  light,  and  is  thereby  covered 
tvith  red  coating. 

80.  Water  as  a  Solvent.  —  Ex.  45.  Fill  a  test-tube, 
or  small  beaker,  about  half  full  of  water ;  sprinkle  into 
it  a  small  quantity  of  finely  powdered  copper  sulphate,  and 
shake  or  stir  it  vigorously.  The  blue  salt  will  impart  its  own 
color  to  the  water ;  and,  if  too  much  has  not  been  added,  the 
solid  will  wholly  disappear.  A  blue  transparent  liquid 
remains  :  this  is  a  solution  of  copper  sulphate. 

Ex.  46.  To  the  solution  just  made,  if  it  be  quite  trans- 
parent, add  a  little  more  of  the  salt,  and  again  agitate  it. 
Eepeat  this  operation,  if  necessary,  until  the  last  portion 
added  remains  undissolved.  The  clear  blue  liquid  is  then  a 
saturated  cold  solution  of  copper  sulphate. 

Ex.  47.  Apply  the  heat  of  a  lamp-flame  to  the  vessel 
containing  the  saturated  cold  solution.  It  will  be  found  that 
the  undissolved  sulphate  in  the  bottom  will  disappear.  Then 
add  more  :  in  a  little  time  that  too  will  be  dissolved,  showing 
that  heat  increases  the  solubility  of  copper  sulphate. 

Ex.  48.  Continue  to  add  the  powdered  sulphate  to  the 
hot  liquid  until  it,  at  length,  refuses  to  dissolve.  The  quan- 
tity to  be  added  may  be  surprising  ;  but  finally  the  liquid  will 
take  no  more,  and  then  it  is  said  to  be  a  saturated  hot 
solution.  Let  it  stand  until  cold. 

82.  Filtration. —  Ex.  49.  Into  a  small  beaker  of  water 
put  enough  of  the  copper  sulphate  solution,  obtained  above, 
to  give  a  slight,  but  distinct,  blue  tint ;  and  then  add  some 


264  CHEMISTRY. 

solution  of  potassium  ferrocyanide,  as  long  as  the  precipitate 
is  increased  by  the  addition.  Notice  the  abundant  dark- 
brown  precipitate  suspended  in  the  liquid.  Treat  this  fluid 
as  described  in  paragraph  82,  Fig.  44.  A  clear  and  colorless 
liquid  falls  into  the  bottle. 

Ex.  50.  Distillation.  —  A  small  quantity  of  water  may 
be  distilled  in  the  apparatus  represented  in  Fig.  50.  Let 
water  be  poured  in  until  the  retort  is  nearly  half  full,  and  then 
heat  it  to  boiling.  Keep  the  flask,  into  which  the  beak  of  the 
retort  is  thrust,  cold  by  a  stream  of  cold  water,  as  repre- 
sented, or  by  pouring  cold  water  from  a  pitcher.  The 
distilled  water  will  collect  in  the  flask. 

91.  Effects   of   Heat   on    Sulphur.  —  The    statements 
made  in  the  text  may  be  very  easily  verified  in  the  manner 
described.     Apply  the  heat  carefully,  and  raise  the  tempera- 
ture gradually. 

92.  Crystals  by  Solution.  —  Ex.   51.     If  the   hot  satu- 
rated solution  of  copper  sulphate  be  examined  when  cold,  a 
mass  of  blue  crystals  will  be   found.     The  clear  blue  liquid 
which  remains,  is  a  cold  saturated  solution,  and  the  crystals 
are   the   excess  which   hot  water  can  dissolve.     If   merely 
warm  water  instead  of  boiling  water  be  used,  this  excess  will 
be  smaller,  and  the  crop  of  crystals,  on  cooling,  will  be  also 
smaller.     In  this  case  they  will  be  more  distinctly  defined. 

Ex.  52.  Make  a  warm  saturated  solution  of  mercuric 
chloride.  On  cooling,  it  will  deposit  a  crop  of  needle-shaped 
crystals. 

Ex.  53.  Make  a  warm  saturated  solution  of  potassium 
nitrate.  On  cooling,  fine  prismatic  crystals  will  appear. 

Ex.  54.  Dissolve  a  little  copper  chloride  in  alcohol, 
making  a  saturated  solution.  Pour  this  solution  over  a  per- 
fectly dean  glass  plate,  and  let  the  excess  run  off,  leaving 
only  a  film  upon  the  surface.  In  a  few  moments  a  beautiful 
crystallization  will  begin,  and  spread  rapidly  over  the  plate. 

Ex.  55.     Use  a  saturated  solution  of  ammonium  chloride  in 


APPENDIX.  265 

water,  to  flow  over  the  plate.  Then  gently  warm  the  glass 
over  the  lamp,  and  afterward  watch  the  growth  of  crystals. 

93.  Sulphur  and  Iron. —  Ex.  56.  Mix  very  intimately 
four  grams  of  sulphur  with  seven  grams  of  the  finest  iron- 
filings,  and  put  the  mixture  into  an  ignition- tube,  that  is,  a 
test-tube  made  of  hard  glass.  Then  apply  heat  to  the  lower 
end  of  the  tube.  Shortly  the  mixture  will  begin  to  glow,  on 
account  of  the  chemical  action  between  the  sulphur  and  the 
iron.  After  the  action  has  well  started,  withdraw  the  tube 
from  the  flame,  and  the  ignition  will  continue  until  the  con- 
tents have  been  completely  changed  into  iron  sulphide. 

98.  Precipitates  by  Sulphuretted  Hydrogen.  —  Ex. 

57.  Into  one  test-glass  put  a  dilute  solution  of  copper  sul- 
phate, into  a  second  put  a  dilute  solution  of  arsenious  oxide, 
and  into  a  third  put  a  dilute  solution  of  zinc  sulphate.  Add 
a  few  drops  of  hydrochloric  acid  to  the  first  two  solutions, 
and  some  ammonia  to  the  third.  Finally,  add  to  each  some 
of  the  solution  of  sulphuretted  hydrogen,  made  in  the  way 
represented  by  Fig.  47. 

In  the  first     will  appear  a  black    precipitate  of    copper  sulphide, 
In  the  second  "          "        yellow  "         arsenious  sulphide, 

In  the  third     "         "        white  "  zinc  sulphide. 

103.  Nitric  Acid  an  Oxidizing  Agent.  —  Ex.  58.  Take 
a  piece  of  tin-foil,  about  two  inches  square,  fold  it  loosely, 
and  place  it  in  a  porcelain  cup  or  small  beaker.  Then  add  a 
small  quantity  of  nitric  acid.  Very  soon  a  violent  action 
will  begin,  resulting  in  volumes  of  red  fumes,  which  escape 
into  the  air,  and  a  moist  white  powder  in  the  dish.  This 
white  powder  is  the  tin  oxide  into  which  the  tin  has  been 
converted  by  the  acid. 

105.  Sulphuric  Acid  and  Water.  —  In  mixing  strong 
sulphuric  acid  and  water,  always  pour  the  acid  into  the 
water,  never  the  water  into  the  acid.  The  fluid  should  be 
constantly  stirred  while  the  acid  is  being  added. 


CHEMISTRY. 

111.  Preparation  of  Nitrogen.  —  Ex.  59.     Let  the  top 

of  a  cork  be  made  slightly  concave  with  a  sharp  knife,  and 
then  let  it  be  thoroughly  rubbed  with  powdered  crayon  or 
chalk.  Cut  from  the  end  of  a  stick  of  phosphorus  under 
water  a  piece  as  large  as  a  small  pea,  and  dry  it  completely 
by  very  gently  pressing  it  for  a  moment  between  the  folds  of 
a  piece  of  blotting  or  filter  paper.  Place  the  prepared  cork 
on  the  water  over  the  shelf  of  the  cistern,  and  lay  the  phos- 
phorus upon  it.  Next  touch  the  phosphorus  with  a  hot  wire, 
and  immediately  invert  over  it  a  gallon  jar.  See  Fig.  49,  and 
the  text  accompanying  it. 

It  will  be  well  to  have  a  jar  of  the  gas  prepared  before- 
hand,-with  which  to  illustrate  the  properties  of  the  gas.  This 
will  obviate  the  necessity  of  waiting  for  the  absorption  of  the 
phosphoric  vapors. 

Ex.  60.  Lightness  of  Nitrogen.  —  Fill  a  small  jar  with 
the  gas,  slip  a  glass  plate  under  its  mouth,  and  lifting  it  from 
the  water,  keeping  its  mouth  downward,  thrust  a  lighted 
taper  up  into  it.  The  flame  will  be  extinguished. 

The  result  not  only  shows  that  nitrogen  will  not  support 
combustion,  but  also  that  it  is  lighter  than  air. 

Ex.  61.  Fill  the  jar  again,  and,  slipping  the  glass  plate 
under  it  as  before,  lift  it  from  the  water,  place  it  mouth 
upward  on  the  table,  and  remove  the  plate.  Leisurely  light 
a  taper,  and  finally  thrust  it  into  the  jar.  The  flame  will  not 
be  extinguished  this  time,  which  shows  again  that  nitrogen  is 
lighter  than  air. 

126.  Nitrous  Oxide.  —  Ex.  62.  Having  filled  some 
small  jars  with  nitrous  oxide,  by  the  experiment  described  in 
connection  with  Fig.  51,  remove  one  to  the  table,  on  which 
let  it  stand  mouth  upward.  Slide  its  cover  to  one  side,  and 
insert  a  lighted  taper.  The  flame  instantly  enlarges,  con- 
tinues with  vigor,  and  is  surrounded  by  a  hazy  envelope. 

Ex.  63.  Lower  into  another  jar.  of  the  gas  a  combustion- 
spoon,  containing  a  bit  of  ignited  phosphorus,  and  notice 


APPENDIX.  267 

that  the  combustion  will  proceed  with  almost  as  great  bril- 
liancy as  in  oxygen. 

127.  Nitric  Oxide.  —  Ex.  64.  Remove  a  small  jar  of 
this  gas  to  the  table,  and  plunge  a  lighted  taper  into  it :  the 
flame  will  be  extinguished. 

Ex.  65.  Place  a  bit  of  phosphorus  in  a  combustion- 
spoon,  and  ignite  it.  When  the  combustion  is  well  started, 
plunge  the  phosphorus  into  a  jar  of  nitric  oxide  :  the  phos- 
phorus will  continue  to  burn  with  great  brilliancy. 

129.  Nitric  Peroxide.  —  Ex.  66.  Let  a  jar  be  about 
half  filled  with  nitric  oxide,  and  place  it  so  that  its  mouth 
projects  over  the  edge  of  the  shelf  on  which  it  stands  in  the 
cistern.  Pour  air  from  another  small  jar  up  into  it,  and 
notice  the  cherry-red  vapor  which  instantly  appears.  The 
greater  part  of  this  red  vapor  is  nitric  peroxide. 

Or  the  jar  containing  the  nitric  oxide  may  be  simply  lifted 
a  little  to  let  air  bubble  under  one  edge  into  it.  The  red 
vapors  will  increase  with  every  bubble. 

137.  Diffusion  of  Liquids.  —  Ex.  67.  Make  the  ex- 
periment represented  by  Fig.  43,  and  mark  the  height  of 
the  vial  in  the  jar.  Then  leave  the  whole  standing  quietly 
for  twenty- four  hours,  and  notice  that  the  vial  stands  higher. 
The  salt  water  has  diffused  upward,  lifting  the  vial  with  it. 

Ex.  68.  Osmose  of  Liquids.  —  Fill  a  wide-mouthed  vial 
with  a  strong  solution  of  potassium  chromate,  and  tie  a  piece 
of  bladder  over  it,  so  as  to  close  it  completely.  The  vial 
should  be  full,  and  the  bladder  in  contact  with  the  fluid ;  but 
not  the  least  portion  of  the  solution  should  be  on  the  outside. 
Stand  this  bottle  on  the  bottom  of  a  large  beaker,  and  then 
nearly  fill  the  beaker  with  water.  Let  the  apparatus  stand 
for  twenty-four  hours,  when  it  will  be  found  that  the  water  is 
colored  throughout,  showing  that  the  salt  has  passed  through 
the  membrane,  to  diffuse  through  the  fluid  outside. 

Other  salts  may  be  treated  in  the  same  way,  and  their  dif- 
fusion through  the  membrane  compared 


268  CHEMISTRY. 

141.  Phosphorus.  —  Phosphorus  should  never  be  handled 
without  the  greatest  care  being  taken  to  guard  against 
igniting  it.  Handle  it  with  forceps,  and  cut  it  when  under 
water. 

Ex.  69.  Phosphorescence.  —  Place  a  clean  stick  of 
phosphorus  in  a  dark  room  :  it  will  emit  a  pale,  pearl-like 
light.  If  the  phosphorus  is  old,  and  covered  with  a  red 
coating,  it  should  first  be  immersed  in  water.,  and  the  red 
surface  removed  by  scraping,  to  expose  the  translucent  sub- 
stance beneath. 

Ex.  70.  Solubility  in  Ether.  —  Put  a  little  ether  into 
a  small  vial,  and  add  a  few  small  pieces  of  phosphorus. 
Allow  it  to  stand,  shaking  it  occasionally,  for  several  hours. 
Much  or  the  whole  of  the  phosphorus  will  dissolve. 

Ex.  71.  Attraction  for  Oxygen.  —  Expose  a  clean 
stick  of  phosphorus  to  the  air,  and  notice  the  clouds  of  white 
vapor  which  fall  away  from  it.  Phosphorus  and  oxygen 
combine  at  ordinary  temperature  to  form  this  phosphorus 
oxide. 

Ex.  72.  Saturate  a  strip  of  filter  or  blotting  paper  with 
the  solution  of  phosphorus  in  ether,  made  in  Ex.  70,  and  hang 
it  conveniently  exposed  to  air.  The  ether  soon  evaporates  ; 
and  then  the  phosphorus  combines  with  oxygen  of  the  air, 
yielding  clouds  of  white  vapor,  and  sometimes  evolving  heat 
enough  to  set  the  paper  on  fire. 

Ex.  73.  Fire  in  Water.  —  Cover  the  bottom  of  an  ale- 
glass  or  a  test-glass  with  potassium  chlorate,  and  add  a  small 
piece  of  phosphorus.  Let  water  be  introduced,  enough  to  fill 
the  glass  two-thirds  full.  Next  fill  a  pipette  with  strong  sul- 
phuric acid ;  close  the  top  of  it  with  the  finger,  and  thrust  the 
lower  end  into  the  water,  and  down  upon  the  chlorate.  Then 
remove  the  finger,  and  allow  some  of  the  heavy  acid  to  flow. 
The  acid  decomposes  the  chlorate,  and  liberates  chlorine  per- 
oxide. This  is  immediately  decomposed  by  the  phosphorus, 
which  takes  its  oxygen,  and  enters  into  a  brilliant  combus- 
tion in  the  water. 


APPENDIX.  269 

153.  Arsenic  Compounds.  —  Ex.  74.  Powder  some 
arsenious  oxide,  As?  O3,  and  heat  it  with  water  in  a  beaker. 
It  is  quite  soluble  in  hot  water.  Saturate  the  hot  solution, 
and  then  allow  it  to  cool  quietly.  Crystals  of  arsenious 
oxide  will  be  deposited,  showing  that  this  substance  is  less 
soluble  in  cold  water. 

Test  the  solution  with  litmus  paper:  it  is  an  acid  solution. 
The  As2O3  is  therefore  an  anhydride. 

Ex.  75.  Arsenious  Oxide  is  Volatile.  —  Take  a  piece 
of  glass  tubing,  about  eight  inches  in  length  and  three- 
sixteenths  of  an  inch  in  diameter ;  hold  its  middle  part  in  a 
gas-flame,  turning  it  constantly  to  heat  all  sides  equally,  and 
when  it  softens  pull  it  apart.  Two  short  tubes,  closed  at  one 
end,  are  thus  obtained. 

Into  one  of  these  tubes  drop  a  very  little  arsenious  oxide 
to  the  bottom,  and  apply  a  gentle  heat.  The  arsenious  oxido 
will  soon  leave  the  bottom  of  the  tube,  and  afterward  will  bp 
found,  as  a  ring  of  white  crystals,  in  the  upper  cold  parts  o> 
the  tube. 

Ex.  76.  Sclieele's  Green. — Put  some  of  the  arsenic 
solution  into  a  test-glass  containing  water.  Next  prepare 
some  ammonio-copper  sulphate,  as  follows :  To  a  dilutf 
solution  of  copper  sulphate  add  ammonium  hydrate  until  thf* 
blue  precipitate  which  is  at  first  formed  is  again  dissolved. 
The  rich  blue  solution  is  the  ammonio-copper  sulphate.  Add 
this  solution,  little  by  little,  to  the  arsenical  solution,  and 
notice  that  a  fine  green  precipitate  is  produced.  This  is 
Scheele's  green,  or  copper  arsenite. 

Ex.  77.  Reinsch's  Test.  —  Add  some  of  the  arsenical 
solution  to  a  test-glass  of  water,  and  add  also  a  drop  or  two 
of  hydrochloric  acid.  Next  insert  a  piece  of  bright  copper 
wire.  In  a  little  while  the  copper  will  be  found  to  be  cov- 
ered with  a  dark  gray  coating.  The  copper  decomposes  the 
arsenical  compound,  and  arsenic  itself  is  deposited  upon  it. 

166.  Carbon  Oxide.  —  The  preparation  of  this  gas  may 


270  CHEMISTRY. 

be  accomplished  with  an  apparatus  fitted  up  as  shown  in  Fig. 
29,  except  that  the  delivery-tube  should  reach  over  to  the 
water-cistern,  so  that  the  gas  may  be  collected  over  water. 

Ex.  78.  Put  about  one  hundred  and  eighty  grains  of 
finely  powdered  potassium  ferrocyanide  into  the  flask,  and 
add  about  ten  times  this  weight  of  strong  sulphuric  acid. 
Then  cork  the  flask,  and  apply  heat.  The  gas  will  be  given 
off  abundantly  ;  and,  after  the  air  has  been  driven  out  of  the 
apparatus,  several  small  jars  or  wide-mouthed  bottles  may  be 
filled  with  it. 

Ex.  79.  Its  blue  Flame.  —  Lift  a  jar  from  the  cis- 
tern, keeping  its  mouth  downward,  and  thrust  up  into  it  the 
flame  of  a  taper.  The  taper  will  be  extinguished  on  entering 
the  gas,  but  the  gas  will  itself  take  fire,  and  burn  with  a  blue 
flame. 

Ex.  80.  Lighter  than  Air.  —  Lift  another  jar  of  the 
gas,  and  turn  its  mouth  upward.  Then  introduce  the  flame 
of  the  taper:  no  combustion  of  gas  follows,  showing  that 
it  has  escaped  upward. 

167.  Carbon  Dioxide.  —  There  is  a  more  simple  method 
of  obtaining  carbon  dioxide  than  that  described  in  the  text, 
which  will  be  good  enough  for  some  purposes.  Thus  :  — 

Ex.  81. — Cover  the  bottom  of  a  jar,  or  wide-mouthed 
bottle,  with  sodium  carbonate,  or  with  small  fragments  of 
marble,  and  pour  a  little  hydrochloric  acid  upon  this  material. 
Vigorous  effervescence  occurs :  carbon  dioxide  is  set  free. 
It  lifts  the  air,  and  finally  itself  fills  the  jar. 

Ex.  82.  It  extinguishes  Flame.  —  Insert  into  the  jar 
containing  the  gas  the  flame  of  a  taper :  it  is  instantly 
extinguished. 

185.  Organic  Substances.  —  Ex.  83.  Take  a  piece  of 
common  paper,  and  roll  it  into  the  form  of  a  compact  ball 
the  size  of  a  small  nut.  Drop  this  to  the  bottom  of  a  test- 
tube,  and  heat  it  in  the  lamp-flame.  The  paper  will  give  off 
white  vapors,  and  a  brownish  liquid  will  condense  on  the 


APPENDIX.  271 

upper  and  cold  parts  of  the  tube  ;  but  notice  particularly  that 
the  paper  becomes  black.  When  no  more  vapors  arise, 
remove  the  black  mass  from  the  tube,  and  notice  that  it  is  brit- 
tle, and  in  all  other  respects  shows  the  properties  of  carbon. 

The  experiment  proves  that  carbon  is  a  constituent  of  this 
organic  substance. 

Ex.  84.  Put  about  two  inches  of  thick  sirup  of  sugar 
into  a  cylinder,  and  stir  into  it  a  nearly  equal  volume  of 
concentrated  sulphuric  acid,  or  "  oil  of  vitriol."  The  acid 
decomposes  the  sugar,  removes  its  hydrogen  and  oxygen, 
but  leaves  its  carbon.  Notice  the  bulky,  coal-black  residue. 
Carbon  is  a  constituent  of  this  organic  substance  also. 

Ex.  85.  Burn  a  bit  of  camphor,  and  hold  a  white  plate  in 
its  flame.  Notice  the  large  deposit  of  carbon  in  the  form  of 
soot.  Camphor  is  an  organic  substance,  and  carbon  is  one 
of  its  constituents. 

187.  Marsh-Gas.  —  Ex.  86.  Marsh-gas  may  be  prepared 
with  the  apparatus  represented  in  Fig.  5.  The  ignition-tube 
should  be  about  eight  inches  long.  It  should  be  charged  with 
as  much  as  needed  of  a  dry  powder,  made  by  mixing  two 
grams  sodium  acetate,  four  grams  caustic  soda,  and  eight 
grams  slaked  lime,  and  gently  heating  on  a  plate  until  the 
water  of  crystallization  of  the  acetate  is  wholly  driven  off. 
The  tube  is  then  to  be  heated.  The  gas  will  be  collected  in 
the  first  flask. 

Na  C2  H3  O2  +  Na  H  O  =  Nag  C  O3  +  C  H4. 

The  lime  is  used  to  render  the  mixture  porous,  and  prevent 
its  fusion. 

Ex.  87.  If  a  larger  quantity  of  the  gas  is  desired,  the 
experiment  may  be  made  with  the  apparatus  shown  in  Fig. 
48.  A  larger  quantity  of  the  mixture  of  acetate,  hydrate, 
and  lime,  is  placed  in  the  retort,  and  the  gas  is  collected  over 
water  in  the  cistern. 

When   experiments   are   to   be   made  with   the   gas,  thfo 


272  CHEMISTKY. 

method  of  preparation  is  better  than  that  given  above. 
Several  small  bottles  may  be  filled  for  examination. 

Ex.  88.  Lift  a  bottle  of  marsh-gas  from  the  cistern, 
keeping  its  mouth  downward,  and  bring  a  lighted  taper 
beneath  it.  The  gas  takes  fire,  and  burns  with  a  yellow 
flame. 

Ex.  89.  Lift  a  bottle  of  the  gas  from  the  water,  turn  its 
mouth  upward,  and,  a  moment  or  two  afterward,  insert  a 
lighted  taper.  No  combustion  of  the  gas  follows.  The  gas 
has  escaped,  showing  its  lightness. 

Ex.  90.  Lift  a  bottle  of  the  gas  from  the  cistern,  and, 
holding  a  lighted  taper  in  the  other  hand,  turn  the  bottle 
mouth  upward  just  under  the  flame.  The  gas  rising  out  of 
the  jar  comes  in  contact  with  the  flame,  and  burns. 

191.  Alcohol.  —  Ex.  91.  Dissolve  ten  grams  of  honey 
in  a  liter  of  water,  and  add  a  little  brewer 's-yeast.  Fill  a 
small  flask  with  the  solution.  Close  the  flask,  and  invert  it 
in  a  dish  containing  enough  of  the  same  sirup  to  cover  the 
mouth  of  it.  Open  it,  and  leave  it  standing  in  a  warm  place 
for  twenty-four  hours.  Notice  then  that  a  colorless  gas  has 
collected  in  the  upper  part  of  the  flask. 

Ex.  92.  Cork  the  flask  while  its  mouth  is  still  under  the 
surface  of  the  sirup :  then  lift  it  away,  and  place  it  upright 
on  the  table.  The  gas  will  now  be  in  the  neck  of  the  flask. 
Remove  the  cork  carefully,  and  insert  the  flame  of  a  match 
or  taper :  it  will  be  instantly  extinguished.  This,  together 
with  the  fact  that  it  is  heavier  than  air,  as  shown  by  its 
remaining  in  the  open  flask,  shows  that  it  is  carbon  dioxide. 

Ex.  93.  Taste  the  fluid  in  the  flask :  it  will  be  found  to 
have  the  flavor  of  alcohol. 

Ex.  94.  Close  the  flask  with  a  cork  provided  with  a 
delivery- tube,  such  as  may  be  seen  represented  in  Fig.  59  ; 
but  instead  of  letting  the  end  of  the  tube  dip  into  water,  as 
there  shown,  let  it  pass  into  a  second  small  flask  resting  on 
the  water.  Then  apply  heat,  as  in  the  figure,  and  keep  the 


APPENDIX.  273 

second  flask  cold  by  means  of  water.  At  a  temperature  of 
about  90°  C.  the  dilute  alcohol  will  distill  over,  and  be  con- 
densed in  the  second  flask. 

194.  Ktlier. —  Ex.  95.  Upon  a  plate  first  pour  water 
enough  to  well  cover  the  bottom,  and  then  carefully  pour 
ether  upon  one  edge  of  the  liquid,  letting  no  drops  fall  out- 
side the  plate.  The  ether  will  spread  over  the  surface  of  the 
water.  Next  touch  a  match-flame  to  the  surface  at  one  edge, 
and  notice  the  instantaneous  ignition.  The  flames  will  con- 
tinue until  the  ether  is  all  burned  away.  This  shows  very 
prettily  that  ether  is  lighter  than  water,  and  very  combustible. 

Ex.  96.  Pour  two  or  three  cubic  centimeters  of  ether 
into  a  wide-mouthed  bottle  or  tumbler,  and  cover  it  loosely. 
After  a  few  moments  remove  the  cover,  and  apply  the  flame 
of  a  match.  The  vapors  of  ether  will  take  fire,  and  burn 
with  a  flash.  Hence  ether  is  very  volatile,  and  its  vapors  are 
heavier  than  air. 

Ex.  97.  Pour  a  few  drops  of  ether  on  the  bulb  of 
apparatus  (Fig.  1 ) ,  and  notice  the  rise  of  the  liquid  in  the 
tube  below.  The  rapid  evaporation  of  the  ether  absorbs 
heat,  and  cools  the  bulb  and  the  air  within. 

196.  Olefiant  Gas.  —  Ex.  98.  For  the  preparation  of 
this  gas,  the  apparatus  shown  in  Fig.  36  may  be  used.  The 
flask  should  be  large  :  one  holding  a  liter  may  be  used  with 
the  following  quantity  of  materials,  but  in  any  case  it  should 
not  be  more  than  one-third  full.  Into  the  flask  put  fifty 
cubic  centimeters  of  alcohol,  and  add  two  hundred  cubic  cen- 
timeters of  strong  sulphuric  acid.  Shake  the  mixture  well, 
and  then  place  the  cork  in  the  neck  of  the  flask,  and  apply  a 
gentle  heat.  The  chemical  action  quickly  begins.  Ether  is 
set  free  at  first,  but  ethylene  soon  takes  its  place.  Hence  the 
first  portions  of  gas  may  be  allowed  to  escape  before  the 
receiver  is  brought  over  the  end  of  the  delivery-tube  to  catch 
the  ethylene. 

Watch  and  regulate  the  heat,  so  that  the  liquid  may  not 


274  CHEMISTRY. 

froth  up  too  much  in  the  flask,  and  do  not  keep  the  operation 
going  too  long,  since  sulphurous  acid  is  produced  in  the  last 
stages  of  the  reaction. 

Ex.  99.  Lift  a  jar  of  the  gas  from  the  cistern,  mouth 
downward,  and  thrust  a  lighted  taper  up  into  it :  the  gas 
takes  fire  at  the  mouth  of  the  jar,  and  burns  with  a  bright 
flame.  Turn  the  jar  mouth  upward  while  the  gas  is  burn- 
ing, and  the  flame  will  be  fed  by  the  gas  escaping  upward. 
It  is  a  little  lighter  than  air  (.978). 

227.  Flame  Tests  for  Potassium  and  Sodium.  —  Ex. 

100.  Bend  the  end  of  a  platinum  wire  into  a  loop,  moisten 
it,  and  gather  some  powdered  potassium  compound,  as  potas- 
sium chloride,  upon  it,  and  then  thrust  it  into  the  edge  of  a 
colorless  gas-flame,  or  even  of  an  alcohol-flame.  Notice  the 
fine  violet  color  imparted. 

Ex.  101.  Clean  the  platinum  wire,  and  use  it  again  in  the 
same  way,  with  some  compound  of  sodium,  —  sodium  chloride 
for  example,  —  and  notice  the  rich  yellow  color  imparted  to 
the  flame. 

Ex.  102.  Make  a  strong  solution  of  sodium  chloride  in 
alcohol.  Fix  a  small  tuft  of  cotton  on  the  end  of  a  wire, 
and  wet  it  with  this  solution.  By  touching  a  match-flame  to 
the  tuft,  a  fine,  large  flame  will  be  produced,  which  shows  the 
yellow  color  to  good  advantage. 

233.  Lime- Water.  —  Ex.  103.  Into  a  bottle  of  clear 
water  put  a  small  quantity  of  lime,  and  shake  it  thoroughly. 
A  little  of  the  lime  will  dissolve.  Pour  the  milky  liquid  upon 
a  filter :  the  clear  and  colorless  filtrate  is  lime-water. 

235.  Calcium  Carbonate.  —  Ex.  104.  Fill  a  test-glass 
one-fourth  full  of  lime-water,  and  dilute  it  with  an  equal 
quantity  of  water.  Pass  carbon  dioxide  through  this  solu- 
tion, by  means  of  the  apparatus,  Fig.  69,  by  putting  the  end 
of  the  delivery-tube  into  the  test-glass.  Notice  that  the  fluid 
soon  becomes  milky :  this  is  owing  to  the  production  of  cal- 


M 

D!^  I  V  JS  R  SI1       275 


cium  carbonate,  which  is  insoluble  in  water,  and  appears  as  a 
white  precipitate. 

Ca(HO)2  +  CO2  =  CaCO3  +  H2O. 

Ex.  •  105.  Solubility  of  the  Ca  CO3.  —  Continue  the 
stream  of  carbon  dioxide,  and  after  a  time  notice  that  the 
whiteness  of  the  liquid  is  diminished.  Indeed,  after  a  while 
the  solution  may  become  again  quite  clear.  The  carbonate 
which  formed  at  first  is  dissolved. 

Ex.  106.  To  restore  the  Carbonate.  —  Put  this  clear 
solution  of  the  carbonate  in  a  flask,  and  boil  it  for  some  time. 
Notice  that  it  becomes  turbid  again.  The  carbon  dioxide  is 
driven  away  by  the  heat,  and  the  water  can  no  longer  hold 
the  carbonate  in  solution.  Hence  it  re-appears. 

Ex.  107.  A  Class-Test  for  the  Group.  —  Prepare 
three  test-glasses,  one  with  a  solution  of  calcium  chloride, 
another  with  strontium  chloride,  and  the  third  with  barium 
chloride.  Into  each  pour  a  little  ammonium  carbonate. 
Notice  that  a  white  precipitate  at  once  forms.  The  com- 
pounds of  these  metals  behave  alike  toward  ammonium 
carbonate  :  they  are  converted  into  carbonates,  which  are 
precipitated. 

Ex.  108.  The  Flame-Tests.  —  Prepare  a  strong  solu- 
tion of  each,  barium  chloride,  strontium  chloride,  and  cal- 
cium chloride.  Soak  a  piece  of  pumice  in  each,  and  then 
with  a  pair  of  forceps  hold  them,  successively,  in  the  color- 
less gas-flame.  The  barium  compound  yields  a  delicate 
green  flame  ;  the  calcium  compound,  a  pale  rose-red  ;  and 
the  strontium  compound,  a  fine  crimson. 

237.  To  precipitate  Aluminium  Hydrate.  —  Ex.  109. 
Prepare  a  solution  of  aluminium  sulphate  or  of  alum  in  a 
test-glass,  and  add  ammonia,  little  by  little.  A  gelatinous 
white  precipitate  falls  :  this  is  the  aluminium  hydrate, 
A12  (H  0)6. 

Ex.   110.     Caismine  Lake.  —  Boil  a    little    cochineal   in 


276  CHEMISTRY. 

a  small  flask  of  water  until  the  coloring  matter  is  extracted. 
Filter  this  solution  into  a  test -glass,  or  beaker.  Add  to  this 
colored  water  about  an  equal  volume  of  aluminium  sulphate 
or  alum.  Finally  add  ammonia.  A  colored  precipitate  is  at 
once  produced,  which,  on  settling,  leaves  the  solution  quite 
or  nearly  colorless. 

The  ammonia  precipitates  the  aluminium  hydrate  as  in  the 
preceding  experiment.  But  this  hydrate  has  a  strong  attrac- 
tion for  the  coloring  matter  of  the  cochineal,  and  carries  it 
along  with  itself.  The  colored  precipitate  is  called  CARMINE 
LAKE. 

Ex.  111.  Other  Lakes.  —  Almost  any  other  organic 
coloring  matter  may  be  used  instead  of  the  cochineal.  A 
colored  precipitate  will  be  produced :  all  such  are  called 
LAKES. 

It  is  this  power  of  aluminium  hydrate  to  precipitate  color- 
ing matter,  that  renders  aluminium  sulphate  and  alum  useful 
in  the  arts  of  dyeing  and  calico-printing. 

240.  Compounds  of  Iron.  —  Iron  forms  two  large  and 
important  classes  of  compounds,  called  respectively  the 
FERROUS  compounds  and  the  FERRIC  compounds. 

Ex.  112.  The  Ferrous  Hydrate.  —  Boil  a  little  water 
in  a  beaker,  to  expel  its  dissolved  air,  and  then  dissolve  in 
it  a  few  small  crystals  of  ferrous  sulphate  (green  vitriol). 
Select  those  which  are  green,  without  white  spots.  Into 
another  beaker  put  a  little  solution  of  potassium  hydrate, 
and  boil  it  also,  to  expel  the  air  which  it  holds  in  solution. 
Finally  pour  the  two  solutions  together,  and  notice  the  pro- 
duction of  a  copious  white  or  greenish-white  precipitate  :  this 
is  ferrous  hydrate,  Fe  (H  O)2.  When  pure,  it  is  white :  in 
presence  of  air,  it  becomes  green. 

Ex.  113.  The  Ferric  Hydrate.  —  Make  a  solution  of 
ferrous  sulphate  in  water,  add  a  few  drops  of  strong  nitric 
acid,  and  then  heat  to  the  boiling-point.  Finally  add 
potassium  hydrate.  Instead  of  the  whitish-green  precipitate 


APPENDIX.  277 

obtained  before,  a  copious  red-brown  precipitate  is  produced : 
this  is  the  ferric  hydrate,  Fe2  (H  O)6. 

The  nitric  acid  changed  the  ferrous  into  the  ferric  sulphate. 

Ex.  114.  Test  for  Ferrous  Compounds.  —  Select  a  per- 
fect blue-green  crystal  of  ferrous  sulphate,  and  dissolve  it  in 
recently  boiled  water.  Divide  the  solution  into  two  parts. 
To  one  part  add  a  little  potassium  ferrocyanide,  and  notice 
the  pale-blue  precipitate  which  appears. 

To  the  other  part  add  a  little  potassium  ferricyanide,  and 
notice  the  fine  dark-blue  precipitate  of  ferrous  ferricyanide. 

Pale-blue  precipitates  with  ferrocyanide,  and  dark-blue 
precipitates  with  ferricyanide,  are  given  by  the  ferrous  com- 
pounds. 

Ex.  115.  Test  for  Ferric  Compounds.  —  Add  a  few 
drops  of  nitric  acid  to  a  solution  of  ferrous  sulphate,  and 
heat  it  to  boiling,  in  order  to  change  it  into  ferric  sulphate, 
and  divide  the  solution  into  two  parts. 

Add  to  one  part  a  little  potassium  ferrocyanide,  and  notice 
the  rich  blue  precipitate  of  "  Prussian  blue  "  which  instantly 
appears. 

Add  to  the  other  part  a  little  ferricyanide,  and  notice,  that 
while  the  liquid  becomes  colored,  yet  no  precipitate  is  pro- 
duced. 

Deep-blue  precipitates  with  ferrocyanide,  and  no  precipi- 
tates with  ferricyanide,  are  given  by  the  ferric  compounds. 

Ex.  116.  To  dye  Cloth  Blue.  —  Make  a  solution  of 
ferric  sulphate  by  adding  a  little  nitric  acid  to  ferrous  sul- 
phate, and  heating  the  mixture  to  the  boiling-point.  In 
another  beaker  make  a  solution  of  potassium  ferrocyanide. 
Dip  a  piece  of  white  cotton  cloth  into  the  ferric  sulphate,  and 
afterward  immerse  it  in  the  ferrocyanide.  Prussian  blue  will 
be  precipitated  upon  every  fiber  of  the  cloth,  and  color  it 
permanently  blue. 

Prussian  blue  is  largely  used  in  the  arts  of  dyeing  and 
calico-printing. 

Ex.  117.     To  dye  Cloth  Black.  —  Make  a  weak  solution 


278  CHEMISTRY. 

of  tannic  acid  in  water,  in  one  beaker,  and  a  solution  of 
ferrous  sulphate  in  another.  Bring  a  little  of  the  two 
together  in  a  test-glass,  and  notice  the  dark- colored  precipi- 
tate formed.  This  precipitate  becomes  black  on  exposure  to 
air.  It  is  the  ferric  tannate. 

Ex.  118.  Saturate  a  piece  of  cotton  cloth  in  the  solution 
of  tannic  acid,  and  let  it  dry.  Immerse  the  dried  cloth  in 
the  ferrous  sulphate,  and  hang  it  up  exposed  to  air.  Ferric 
tannate  will  be  precipitated  upon  the  fibers  of  the  cloth,  and 
dye  them  black. 

Ex.  119.  Tannic  Acid  in  Tea.  —  Let  a  few  tea-leaves 
be  boiled  in  a  small  quantity  of  water.  Pour  the  clear  solu- 
tion into  a  test-glass,  and  add  a  few  drops  of  ferrous  sul- 
phate. The  liquid  blackens,  and  on  standing  it  will  deposit 
a  precipitate  of  ferric  tannate. 

In  the  same  way  one  may  detect  the  existence  of  tannic 
acid  (tannin)  in  coffee,  in  the  husk  of  the  horse-chestnut,  in 
oak-bark,  or  in  sumach. 

253.  Compounds  of  Lead. — Ex.  120.  Into  a  test-glass, 
containing  strong  nitric  acid,  put  some  clippings  of  metallic 
lead.  A  violent  chemical  action  soon  sets  in,  with  the  evolu- 
tion of  volumes  of  red  vapors.  The  lead  is  converted  into 
lead  nitrate,  which  remains  dissolved  in  the  liquid. 

Ex.  121.  Add  a  considerable  quantity  of  the  lead,  enough 
to  use  up  all  the  acid,  and  put  the  test-glass  outside  the 
window,  so  that  the  fumes  may  not  fill  the  room,  and  let  the 
action  go  on  as  long  as  it  will. 

The  liquid  which  may  be  poured  off  clear,  or  filtered  if 
necessary,  contains  the  nitrate,  which  may  be  used  in  other 
experiments.  It  will  be  well  to  make  this  experiment  before- 
hand, so  that  the  nitrate  may  be  ready  for  use  when  wanted. 

Ex.  122.  Lead  Chloride. —  Into  a  beaker  put  a  tea- 
spoonful  of  the  nitrate  solution,  and  add  one  hundred  cubic 
centimeters  of  water.  Then  add  a  little  hydrochloric  acid, 
as  long  as  a  precipitate  forms.  This  white  precipitate  is  the 
lead  chloride. 


APPENDIX.  279 

Ex.  123.  Obtained  iii  Crystals. — Heat  the  beaker  until 
its  contents  boil,  and  notice  that  the  chloride  dissolves  to  a 
clear  solution.  Then  place  the  beaker  aside,  where  it  will  be 
undisturbed,  and  let  it  cool.  By  and  by  examine  it,  and 
notice  the  needle-shaped  crystals  of  chloride  which  have  been 
deposited. 

This  compound  is  very  soluble  in  hot  water,  slightly  in  cold 
water,  and  the  excess  crystallizes. 

PLx.  124.  Lead  Iodide.  —  Into  a  beaker  containing  water 
put  another  small  portion  of  the  lead  nitrate  solution,  and 
add  to  this,  drop  after  drop  of  potassium  iodide.  Each  drop 
produces  an  additional  quantity  of  the  rich  yellow  precipitate 
of  LEAD  IODIDE. 

Ex.  125.  Obtained  in  Crystals.  —  Add  a  few  drops  of 
hydrochloric  acid  to  the  contents  of  the  beaker,  and  heat  to 
boiling.  The  iodide  dissolves.  Stand  the  beaker  in  cold 
water,  or  let  a  stream  of  cold  water  run  upon  it  to  hasten  its 
cooling,  and  watch  the  result.  The  iodide  separates  from 
the  liquid  ;  and,  on  holding  the  beaker  up  to  the  light,  multi- 
tudes of  brilliant  crystalline  scales  will  be  seen  reflecting  all 
the  colors  of  the  rainbow. 

Ex.  126.  Lead  Cliromate.  —  Fill  a  tall  cylinder  three- 
fourths  full  of  water,  and  add  fifty  cubic  centimeters  of  lead 
nitrate.  Add  a  solution  of  potassium  chromate,  little  by  little, 
and  notice  the  fine  yellow  cloud-like  masses  of  LEAD  CHRO- 
MATE which  roll  downward  towards  the  bottom  of  the  jar. 

Ex.  127.  Action  of  Lead  on  Water.  —  Two  days  be- 
fore this  subject  is  reached,  prepare  the  experiment  ao 
follows  :  — 

Into  each  of  two  bottles  put  some  clippings  of  lead  :  the 
surfaces  should  be  bright.  Fill  one,  two-thirds  full  of  rain- 
water, and  the  other  with  spring-water.  It  is  likely  that  the 
rain-water  will  be  found  to  be  turbid,  and  that  the  spring- 
water  will  remain  clear. 

Or  a  little  ammonium  nitrate  may  be  purposely  added  to 
the  rain-water,  and  a  little  potassium  carbonate  to  the  spring- 
water,  by  which  these  results  are  facilitated. 


280  CHEMISTRY. 

255.  Compounds  of  Copper.  —  Ex.  128.  Fill  a  dinner- 
plate  nearly  full  of  water,  and  in  the  middle  of  it  stand  a 
test-glass.  Put  some  clippings  of  copper  into  the  glass,  and 
pour  upon  them  moderately  dilute  nitric  acid,  a  little  more 
than  enough  to  cover  them.  At  once  invert  over  the  glass  a 
large  receiver  (shown  in  Fig.  20).  A  violent  action  quickly 
begins.  The  air  in  the  receiver  becomes  cherry-red.  The 
fluid  in  the  test-glass  becomes  intensely  blue.  The  red  fumes 
will,  for  the  most  part,  be  dissolved  in  the  water,  and  thus  be 
prevented  from  escaping  into  the  room  ;  and,  if  a  little  blue 
litmus  is  put  into  the  water,  another  change  of  color  will  be 
witnessed,  from  blue  to  red. 

The  blue  liquid  in  the  test-glass  is  a  solution  of  copper 
nitrate.  Pour  it  off  from  the  residue  of  copper  into  a  small 
beaker. 

Ex.  129.  Copper  Hydrate.  —  Add  a  few  drops  of  this 
nitrate  solution  to  a  test-glass  of  water,  and  then,  drop  by 
drop,  ammonia,  and  observe  the  pale-blue  precipitate :  it  is 
copper  hydrate. 

But  continue  to  add  the  ammonia,  and  the  pale-blue  pre- 
cipitate will  begin  to  disappear.  It  dissolves,  a  fine  rich  blue 
liquid  being  obtained. 

Ex.  130.  To  a  test-glass  of  water,  first  add  some  drops 
of  solution  of  copper  sulphate,  often  called  "  blue  vitriol," 
and  then  carefully  add  ammonia.  The  same  pale-blue  hydrate 
is  precipitated.  Continue  the  addition  of  the  ammonia,  and 
the  hydrate  dissolves  in  the  excess  as  before,  yielding  a 
transparent  liquid  with  beautiful  azure-blue  color.  The  rich- 
ness of  this  color  may  appear  to  better  advantage  by  diluting 
the  liquid.  For  this  purpose  pour  it  into  a  beaker,  and  add 
water  until  the  light  can  be  seen  through  the  solution. 

This  is  a  very  sensitive  test  for  copper  salts.  A  very 
minute  quantity  can  be  detected  by  this  ammonio- copper 
sulphate  solution. 


APPENDIX. 


281 


No.   1   SET   OF   APPARATUS. 

INCLUDING  EVERY  ARTICLE  NEEDED  FOR  THE  ONE  HUNDRED  AND 
THIRTY   "EXPERIMENTS   FOR  THE   CLASS-ROOM." 


1  Bunsen's  burner. 

1  forceps  (steel). 

^  dozen  test-tubes  (6-inch) . 

1  test-tube  stand. 

1  pair  adhesive  plates  (glass) . 

1  small  horseshoe-magnet. 

%  dozen  bottles,  saltmouth  (1- 

pint) . 
jr  dozen  bottles,  saltmouth  (^- 

pint) . 
1     mortar     (Wedgwood,     4  - 

in.). 
£  dozen  glass  cylinders  (12  X 

11  inch). 

£  dozen  beakers  ( 1 6-ounce) . 
£  dozen  beakers  (6-ounce). 
1  evaporating-disk  (porcelain, 

8-ounce) . 

1  glass  jar,  tin  cap  (^-gallon). 
1  glass  funnel  (4-inch). 
J  dozen  test-glasses  (4-ounce) . 
^  dozen  bell- jars  (1-pint). 
1  bell- jar  (1 -quart). 
1  bell-jar  (^-gallon). 


1  ignition  side-neck  test-tube 
(8-inch). 

1  tubulated  retort  (1 6-ounce). 

1  battery-jar  (6  X  4J  inch). 

1  combustion-spoon. 

1  pipette. 

1  air-thermometer. 

1  hydrogen  apparatus  (gas 
bottle,  1-pint,  fitted  thistle- 
tube  and  delivery-tube) . 

1  oxygen  apparatus  (flask  8- 
ounce,  fitted  delivery- tube ). 

1  chlorine  apparatus  (flask  8- 
ounce,  fitted  thistle-tube  and 
delivery- tube) . 

1  Woulf's  bottle  (3-neck,  4- 
ounce) . 

1  retort-stand. 

1  pneumatic  cistern. 

\  pound  glass  tubing  (J-inch 
outside) . 

4  feet  rubber  tubing  (J-inch 
mside) . 

1  three-cornered  file. 


CHEMICALS 


NEEDED    FOR    THE    ONE   HUNDRED    AND    THIRTY    "EXPERIMENTS 
FOR  THE  CLASS-ROOM." 


Platinum  wire,  3  inches. 
Magnesium  ribbon,  1  foot. 
Calcium  chloride,  4  ounces. 


Lead  acetate,  1  ounce. 
Potassium  chromate,  1  ounce. 
Copper  sulphate,  4  ounces. 


282 


CHEMISTRY. 


Potassium  ferrocyanide.  J  oz. 
Ferrous  sulphate,  4  ounces. 
Silver  nitrate  solution,  4  oz. 
Lead  nitrate,  J  ounce. 
Sodium  carbonate,  4  ounces. 
Aniline  red,  J  ounce. 
Manganese  dioxide,  ^  pound. 
Bleaching  powder,  J  pound. 
Litmus,  2  ounces. 
Potassium  chlorate,  4  ounces. 
Potassium  iodide,  J  ounce. 
Mercuric  chloride,  1  ounce. 
Potassium  nitrate,  4  ounces. 
Ammonium  chloride,  ^  ounce. 
Ammonium  nitrate,  4  ounces. 
Ammonia,  aqua,  4  ounces. 
Arsenious  acid,  J  ounce. 
Sodium  acetate,  4  ounces. 
Sodium  hydrate,  4  ounces. 
Potassium  chloride,  2  ounces. 


Strontium  chloride,  2  ounces. 
Barium  chloride,  2  ounces. 
Potassium  ferrocyanide,  ^  oz. 
Ammonium  carbonate,  2  oz. 
Sulphuric  acid,  1  pound. 
Hydrochloric  acid,  1  pound 
Nitric  acid,  1  pound. 
Alum,  4  ounces. 
Tannin,  J  ounce. 
Alcohol,  1  quart. 
Ether,  4  ounces. 
Cochineal,  J  ounce. 
Copper  foil,  ^  pound. 
Tin  foil,  i  pound. 
Sulphur,  4  ounces. 
Phosphorus,  2  ounces. 
Iodine,  J  ounce. 
Sodium,  £  ounce. 
Zinc,  granulated,  1  pound. 


No.   2   SET   OF   APPARATUS. 

INCLUDING  ALL  THAT  IS  NEEDED  FOR  THE    FULL  ILLUSTRATION 
OF  THE  TEXT. 

1  No.  1  set  complete. 

2  flasks  (round  bottom,  8-oz.). 
2  flasks  (flat  bottom,  6-oz.). 

1  flask  (round  bottom,  very  light,  1500  cc.). 

1  beaker  (selected,  very  light,  such  size  that  the  1500-cc. 
flask  when  inverted  in  it  will  reach  nearly  to  the  bottom, 
and  close  the  mouth  of  the  beaker  neatly  at  the  same  time) . 

1  bell- jar  (1 -gallon). 

1  glass  crystallizing-basin  (6  inches  diameter). 

1  alcohol  lamp. 


APPENDIX. 

1  decomposing  cell  for  water. 

1  battery  (2  or  4  cells,  Bunsen's  or  Grenet). 

1  electroscope  (pith-ball). 

1  glass  tube  for  friction. 

2  cylinders  (glass,  6  X  1J  in.). 
1  eudiometer  (50  cc.). 

1  induction-coil  (£  in.  spark). 
1  balance  (Robervall's). 

1  set  of  weights  (1  Mlo  down) . 

2  graduated  glass  tubes   (i-inch  diameter,  graduated  to  cc., 
12  inches  long). 

1  retort-holder  (Shelback's). 

1  foot  magnesium  ribbon. 

1  deflagrating  stand. 

1  wire-gauze  spoon. 

1  Woulf's  bottle  (2-necked,  16-ounce). 

1  rubber  bag  (1-gallon). 

1  chloride- calcium  jar  (9-in.). 

2  pinch-cocks. 

1  tripod  (1-ring). 
1  aspirator- bottle  (1-gallon). 
1  reduction-tube  (1-bulb). 
^  dozen  U-tubes  (side-neck  and  corks). 
1  chloride- calcium  tube. 

1  diffusion-of-gases    apparatus,    i.e.,    glass    tube    12   inches 
long,  with  porous  cup  at  one  end. 

1  Hofmann's  apparatus  for  combustion  of  oxygen. 

2  dozen  corks,  assorted. 

4  feet  copper  wire  for  battery  connections. 


284  CHEMISTRY. 


GENERAL   REVIEW.      , 

[The  following  exercises  cover  the  most  important  facts  and  princi- 
ples which  have  been  presented  in  the  foregoing  course  of  chemistry, 
and  may  prove  to  be  useful  as  a  guide  in  conducting  a  general  review 
or  a  final  examination.  It  will  be  seen  that  they  divide  the  subject  into 
five  nearly  equal  parts,  but  that  each  exercise  may  be  easily  divided 
into  two  when  it  is  desirable  to  extend  the  review  over  two  weeks 
instead  of  one.] 

I. 

WHAT  is  an  experiment? 

Describe  two  experiments  which  show  the  difference  be- 
tween mechanical  and  chemical  action. 

Having  two  solid  substances,  how  will  you  proceed  in 
order  to  bring  them  into  chemical  action  ? 

Describe  the  influence  of  heat,  of  light,  and  of  electricity, 
on  chemical  action. 

Prove  that  matter  is  indestructible. 

Give  some  account  of  the  process  of  weighing. 

Give  some  account  of  the  process  of  measuring. 

What  is  analysis  ?     What  is  synthesis  ? 

Describe  an  analysis  of  water,  and  state  the  results. 

Describe  the  synthesis  of  water,  and  state  the  results. 

What  law  of  combination  is  illustrated  by  these  constant 
results  ? 

State  the  law  of  multiple  proportions. 

State  Gay  Lussac's  law  of  volumes. 

State  Avogadro's  law. 

Define  the  following  terms :  molecule,  atom,  combining 
weight,  combining  volume,  specific  gravity. 

Give  the  value  of  each  of  the  foregoing  terms  for  oxygen, 
hydrogen,  and  nitrogen. 

If  there  be  fifteen  grains  of  oxygen,  how  much  hydrogen 
is  needed  to  convert  it  into  water,  and  how  much  water  will 
be  produced  by  their  union  ? 

Show  by  example  the  difference  between  a  symbol  and  a 
formula. 


APPENDIX.  285 

What  are  oxides?  acids?  hydrates?  salts?  How  is  each 
of  these  classes  of  compounds  named? 

What  experiment  will  decide  whether  a  soluble  substance 
is  acid  or  basic  ? 

Let  phosphorus  be  burned  in  dry  air :  give  the  formula 
and  the  name  of  the  product. 

Let  phosphorus  be  burned  in  the  presence  of  water :  give 
the  formula  and  the  name  of  the  product. 

In  the  last  case,  state  all  the  facts  which  the  formula 
teaches  about  the  substance. 

Name  the  constituents  of  hydrosodium  sulphate,  and  give 
its  formula. 

Name  the  substances  whose  formulas  are  K  N  03,  Naa  CO3, 
HNaCO3,  Ca(HO)2,  Fe2O3. 


II. 

Define  element.  What  may  be  said  as  to  the  number  of 
the  elements? 

On  what  principle  are  the  non-metals  classified?  Name 
and  define  the  groups. 

Define  quantivalence. 

Write  the  graphic  symbol  of  chlorine,  oxygen,  nitrogen, 
and  carbon. 

Write  the  graphic  formula  for  hydrochloric  acid ;  for 
water  ;  for  ammonia  ;  for  marsh-gas. 

What  are  such  graphic  formulas  intended  to  show  ?  What 
are  they  not  intended  to  show? 

What  are  all  the  different  kinds  of  formula  which  have 
been  defined  in  this  book  ? 

Describe  two  ways  of  getting  the  hydrogen  from  water. 
Is  there  any  other  way  ? 

What  are  the  physical  properties  of  hydrogen  ?  What  are 
its  chemical  properties  ?  How  does  it  occur  in  nature  ? 

For  what  numerical  values  does  hydrogen  furnish  the 
unit? 


286  CHEMISTRY. 

Define  re-action.  How  are  chemical  changes  represented 
to  the  eye  ? 

Write  the  re-actions  which  occur  in  the  different  experi- 
ments for  preparing  hydrogen. 

Why  does  one  atom  of  zinc  require  two  molecules  of 
hydrochloric  acid  in  chemical  re-action,  while  an  atom  of 
potassium  requires  only  one  ? 

Suppose  we  have  ten  thousand  grains  of  water  at  0°  C., 
and  wish  to  heat  it  to  the  boiling-point  by  a  flame  of  hydro- 
gen, and  that  we  must  make  our  hydrogen  by  means  of  zinc 
and  sulphuric  acid :  how  much  of  these  materials  must  we 
use? 

Name  the  members  of  the  univalent  group  of  non-metals. 
In  what  forms  are  these  elements  found  in  nature  ? 

Compare  the  physical  properties  of  these  elements. 

Compare  their  chemical  properties. 

For  what  purposes  are  the  compounds  of  these  elements 
used  in  the  arts  ? 

Describe  the  preparation  of  chlorine. 

Describe  hydrochloric  acid,  stating  how  it  is  prepared,  its 
properties  and  its  uses. 

What  is  aqua-regia,  and  for  what  is  it  useful? 

From  the  formula  of  hydrochloric  acid,  calculate  its  per- 
centage composition. 

Name  the  members  of  the  bivalent  group  of  non-metals. 
Which  are  of  most  practical  importance  ?  Are  these  impor- 
tant ones  found  abundantly  in  nature  ?  In  what  forms  ? 

Describe  the  preparation  of  oxygen. 

Ten  liters  of  oxygen  are  needed  for  experiment :  how  much 
potassium  chlorate  must  be  used  to  furnish  it  ? 

What  is  the  combining  weight  of  oxygen  ?  its  molecular 
weight?  its  density? 

What  are  the  relations  of  oxygen  to  combustion  and  to  the 
life  of  animals  ? 

Define  allotropism,  and  describe  ozone. 

How  is  the  sulphur  of  commerce  obtained  ?  What  is  ' '  plas- 
tic sulphur ' '  ? 


APPENDIX.  287 

Why  is  sulphur  said  to  be  dimorphous  ? 

By  what  two  general  methods  may  crystals  be  obtained  ? 

III. 

What  important  compounds  do  oxygen  and  sulphur  form 
with  hydrogen  ? 

What  are  the  names  and  the  formulas  for  the  compounds 
of  oxygen  with  chlorine  ? 

What  are  the  names  and  the  formulas  for  the  compounds 
of  sulphur  with  oxygen  ? 

Give  a  complete  description  of  the  electrolysis  of  water  and 
its  results. 

Give  the  freezing-point,  the  boiling-point,  and  point  of 
maximum  density,  of  water,  in  both  Fahrenheit  and  centigrade 
degrees. 

Define  the  terms  solution,  solvent,  soluble,  and  saturated. 

How  may  water  be  purified  from  solid  impurities  ?  From 
volatile  impurities?  Effect  of  freezing? 

What  is  the  difference  between  hard  and  soft  water?  and 
how  may  hard  water  be  softened  ? 

What  is  hydrogen  dioxide  ?     What  is  hydroxyl  ? 

Give  the  preparation  and  properties  of  H2  S,  and  illustrate 
its  re-action  with  metallic  compounds  by  an  example. 

Describe  the  process  of  bleaching  with  sulphurous  oxide. 
What  is  another  substance  used  in  bleaching? 

State  what  you  can  about  sulphuric  acid. 

Define  oxidizing  agent ;  reducing  agent. 

What  is  a  monobasic  acid  ?  A  dibasic  acid  ?  A  normal 
salt?  An  acid  salt? 

Name  and  give  the  symbols  of  the  members  of  the  triva- 
lent  group  of  non-metals. 

Where  is  nitrogen  found  in  nature? 

Describe  the  occurrence  of  phosphorus  in  nature.  Of  ar- 
senic. 

Describe  each  of  these  elements. 


288  CHEMISTRY. 

Give  the  formulas  and  names  of  the  compounds  of  these 
elements  with  hydrogen.  Are  these  compounds  of  practical 
value  ? 

Say  what  you  can  about  the  preparation,  properties,  and 
uses  of  ammonia. 

Give  the  names  and  formulas  of  the  several  oxides  of  ni- 
trogen. Which  of  these  have  corresponding  acids  ?  Describe 
nitric  acid. 

Give  the  composition  of  the  atmosphere  as  completely  as 
you  can.  Why  is  the  atmosphere  a  mixture  rather  than  a 
compound  ? 

Define  and  illustrate  diffusion  and  osmose. 

Describe  "Marsh's  Test"  for  arsenic,  and  point  out  all 
the  chemical  re-actions  which  occur  in  it. 

Name  and  describe  some  of  the  most  common  compounds 
of  arsenic. 

What  is  an  anaesthetic?  Which  of  the  compounds  of  ni- 
trogen with  oxygen  are  anaesthetic  ?  and  how  is  it  prepared  ? 

What  substance  is  an  antidote  to  arsenical  poison  ?  and  how 
may  it  be  prepared?  Name  other  antidotes  which  may  be 
used  instead  if  need  be. 

What  non-metals  constitute  the  quadrivalent  group?  and 
what  are  their  symbols  ? 

What  can  you  say  of  silicon  ? 

What  is  glass  ?  and  from  what  materials  is  it  made  ?  What 
are  the  most  important  varieties  ? 

Give  an  outline  of  the  process  of  making  glass. 

Name  and  describe  the  three  allotropic  forms  of  carbon. 


IV. 

Give  the  names  of  the  compounds  of  carbon  and  oxygen, 
and  their  formulas,  and  describe  the  effect  of  each  when 
breathed. 

Define  combustion,  and  show  what  chemical  action  it  rep- 
resents. 


APPENDIX.  289 

Why  is  it  necessary  to  touch  a  match  to  a  combustible 
before  it  will  burn  ? 

What  are  the  usual  products  of  combustion?  and  why? 

Why  does  wood  burn  with  flame,  while  anthracite  burns 
only  with  a  glow  ?  How  do  you  account  for  the  blue  flame 
which  is  often  seen  over  a  coal  fire  ? 

How  do  we  explain  the  production  of  the  light  in  a  lumi- 
nous flame?  Describe  the  oxyhydrogen  light. 

What  is  the  proper  supply  of  air  needed  to  give  the  full 
heating  effect  of  a  fuel?  How  would  you  calculate  the 
amount  ? 

What  chemical  changes  take  place  in  the  air  and  in  the 
blood  during  respiration  ? 

Explain  the  need  of  ventilating  rooms. 

What  are  the  chemical  changes  which  occur  in  the  process 
of  decay? 

Show  that  combustion,  respiration,  and  decay  are  much 
alike  in  chemical  character. 

Define  organic  chemistry. 

Distinguish  between  organized  bodies  and  organic  sub- 
stances. Which  do  we  study  in  chemistry? 

Define  hydrocarbon.     Define  homologous  series. 

Give  the  formulas  and  names  of  several  members  of  the 
marsh-gas  series. 

What  explanation  of  the  large  number  of  hydrocarbons  is 
given  ? 

Give  the  properties  of  marsh-gas ;  also  of  the  marsh-gas 
s?ries. 

How  are  the  various  commercial  fluids  obtained  from 
petroleum  ? 

How  is  common  alcohol  obtained?  What  are  its  proper- 
ties? Its  composition?  What  is  its  relation  to  ethane ? 

Describe  the  alcohol  series. 

Define  and  illustrate  the  term  radical. 

How  is  common  ether  obtained  ?  What  are  its  properties  ? 
Give  the  general  definition  of  an  ether. 


290  CHEMISTRY. 

What  are  the  olefines  ?     Name  some  of  them. 

Define  and  illustrate  destructive  distillation. 

Name  and  describe  some  of  the  products  of  the  distillation 
of  wood. 

To  what  large  industrial  purpose  is  destructive  distillation 
applied  ?  What  can  you  say  of  the  two  principal  varieties  of 
mineral  coal? 

Trace  the  successive  stages  in  the  manufacture  of  illumi- 
nating gas. 

What  is  benzol?  Nitro-benzol ?  Aniline?  Aniline  red? 
Aniline  dyes  ? 

V. 

Give  the  chemical  meaning  of  the  term  sugar. 

Into  what  three  classes  are  the  sugars  chiefly  grouped? 
Give  examples  of  each. 

Give  the  composition  of  cane-sugar ;  of  starch  ;  of  grape- 
sugar  ;  of  dextrine. 

Define  the  terms  ferment,  fermentation. 

Give  the  chemical  changes  which  occur  first  in  converting 
sucrose  to  glucose,  and  second  in  the  fermentation  of  the 
latter. 

Define  the  terms  ore,  alloy,  native  metal. 

What  are  the  characteristic  properties  of  the  metals  of  the 
alkalies  ?  What  is  an  alkali  ? 

Describe  the  manufacture  of  sodium  carbonate. 

What  are  the  general  properties  of  the  metals  of  the  alka- 
line earths? 

What  can  you  say  of  calcium  oxide  and  its  uses  ? 

Explain  the  formation  of  stalactites  and  stalagmites. 

What  are  alums  ?  Give  the  composition  and  properties  of 
common  alum. 

From  what  ores,  and  in  what  way,  is  zinc  obtained? 

What  can  you  say  of  the  occurrence  of  iron  in  nature? 
Name,  and  state  the  difference  between,  the  forms  of  iron  in 
commerce. 


APPENDIX.  291 

Describe  the  blast-furnace.  Describe  the  process"  of  re- 
ducing iron  ore  in  the  blast-furnace. 

How  are  iron  ' '  castings  ' '  made  ? 

Describe  the  manufacture  of  wrought-iron. 

Describe  the  ' '  Bessemer  process  "of  making  steel  from 
cast-iron. 

Describe  the  method  of  making  steel  from  wrought-iron. 

Say  what  you  can  of  the  occurrence,  extraction,  and  prop- 
erties of  tin. 

Name  the  metals  of  the  antimony  class.  To  what  non- 
metals  are  they  closely  related  ? 

"What  is  type-metal  ?  and  on  what  property  does  its  useful- 
ness depend  ? 

What  is  the  composition,  and  what  are  the  properties,  of 
"fusible  metal"? 

From  what  ore,  and  in  what  way,  is  lead  obtained? 

What  can  you  say  of  the  chemical  action  of  water  in  lead 
pipes  ? 

How  does  copper  occur  in  nature  ? 

What  are  the  chief  ores  of  copper? 

How  is  copper  obtained  from  its  ores  ? 

Name  and  describe  the  most  important  alloys  of  copper. 

From  what  ore,  and  how,  is  mercury  obtained? 

What  are  calomel  and  corrosive  sublimate?  How  can 
these  be  distinguished? 

How  is  silver  extracted  from  argentiferous  galena? 

How  is  silver  obtained  from  other  ores  than  argentiferous 
galena  ? 

What  is  the  composition  of  American  silver  coin? 

What  is  the  action  of  light  on  the  compounds  of  silver? 
Define  photography. 

What  is  the  difference  between  a  negative  and  a  positive 
picture  ? 

How  is  the  negative  made  ?     How  is  the  positive  made  ? 

In  what  condition  does  gold  occur  in  nature  ?     How  is  gold 


292  CHEMISTRY. 

separated  from  gold-bearing  sand?  How  is  it  separated 
from  gold-bearing  quartz  ? 

Where,  and  in  what  form,  is  platinum  found?  What  are 
some  of  its  properties  ? 

Write  out  the  re-action  which  occurs  when  hydrochloric 
acid  is  added  to  silver  nitrate. 

Write  the  re-action  which  takes  place  when  a  silver  plate  is 
held  in  the  vapor  of  iodine. 

Write  the  re-action  which  occurs  when  the  plate  covered 
with  collodion  is  in  the  bath  of  silver  nitrate. 

Write  the  re-action  which  occurs  when  paper  for  the  ' '  posi- 
tive "  is  floated  on  the  two  liquids  needed  for  its  preparation. 

Write  the  re-actions  which  would  occur  if  a  silver  coin 
should  be  placed  in  nitric  acid. 

What  compound  is  formed  when  gold  is  dissolved  in  aqua- 
regia  ? 


INDEX. 


(The  numbers  refer  to  pages.) 

Acids 43 

composition  of 44 

dibasic 110 

hydrogen 45 

oxygen .44 

Acetic  acid 206 

Alcohol .  186 

radicals 189 

Alcohols,  series  of 188 

Alkalies 217 

Allotropism 87 

Alloys 215 

of  antimony 231 

of  bismuth 232 

of  copper 236 

of  mercury    .        .        . 237 

of  silver 239 

Alum 222 

Aluminium 221 

Amalgams 237 

Amalgamation 238 

Amethyst 143 

Ammonia 117 

Ammonia  alum 223 

Amylose 204 

Analysis 23 

Anhydrides 106 

Aniline 200 

dyes 201 

red 201 

Animal  charcoal 149 

Annealing 146 

Antimony 231 

Argand  burner 167 

Arsenic 134,231 

compounds  with  hydrogen 134 

compounds  with  oxygen 136 

293 


294  INDEX. 

Arsenic,  Marsh's  test  for 135 

Reinsch's  test  for 269 

Artiads 58 

Asphalt 199 

Atmosphere 124 

percentage  composition  of 140 

Atom 33 

Atomic  theory 33 

Atomic  weight 35 

of  the  elements 53 

Attraction 10 

Avogadro's  Law 35 

Balance,  the  chemical 20 

Bases 4J 

Bell-metal 236 

Benzine 186 

Benzol 199 

Bessemer  process 229 

Binary  compounds «        ....      36 

names  of 42 

Bismuth 231 

Blastfurnace 226 

Bleaching  with  chlorine 73 

with  sulphur .        .107 

illustrated 260 

powder    .        .        ,        .        .        .        .        .        .  .98 

Bone-black '    .' \   .   V  .  ' .  .;      ..      .  149 

Boracicacid       .        .        .        .  '/.        .       .        .       .*...,  137 

Berates .        .    ,   .        .138 

Borax 137 

Boron ...        .        .        .137 

Brass .236 

Brimstone  .        .        .        .       .     - .       . 102 

Bromine     .        .        .        .       •.,'•;       .        .        .        .        .        .75 

Bronze 236 

Bunsen's  burner 167 

Cadmium 223 

Calcium '    .        .  220 

carbonate 221 

oxide 221 

Carbolic  acid 199 

Carbon .  147 

amorphous 149 

allotropic  forms  of 152 

combustion  of,  in  oxygen 84 

compounds  with  hydrogen 180 

compounds  with  oxygen '.84 


INDEX.  295 

Carbon,  crystallized 150 

dioxide 153 

monoxide 153 

occurrence  in  nature 152 

Carbon  dioxide 153 

a  product  of  combustion 162 

Carbonic  acid 156 

Carboys 109 

Changes,  chemical 2 

physical 1 

Charcoal .  148 

Chemical  action 3 

attraction 10 

combination 4 

decomposition 5 

no  loss  nor  gain  in 17 

Chemistry  defined    . .  6 

an  experimental  science .  7 

Chloric  acid 98 

Chlorine 70 

attraction  of,  for  hydrogen 72 

attraction  of,  for  metals 73 

chemical  character  of                72 

compound  of,  with  hydrogen 76 

compounds  of,  with  oxygen 97 

liquefaction  of 72 

occurrence  of,  in  nature 73 

preparation  of .70 

properties  of 72 

Choke-damp 152 

Classification  of  acids 44 

of  elements 54 

of  metals 215 

of  non-metals 54 

Coal 195 

varieties  of                        202 

Coal  naphtha 199 

Coal  tar 199 

Dalton's  theory 33 

Decay 174 

Deliquescence 218 

Destructive  distillation 192 

application  of 194 

slow 201 

Dextrine 204 

Diamond 150 

Diastase 204 


29b  INDEX. 

Diffusion 127 

Dimorphism 103 

Distillation 94 

destructive 192 

fractional 185 

Electrical  attraction * 10 

Electricity  affecting  chemical  action 14 

Electrolysis 14, 16 

Element  defined 8 

Elements,  atomic  weight  of 53 

classification  of 54, 215 

list  of 53 

metallic 44 

non-metallic .52 

number  of 52 

symbols  of  . .53 

Empirical  formulas .        .59 

Ethane 183 

Ethene 191 

Ether 189 

Ethers,  series  of 190 

Ethyline 191 

Eudiometer 26 

Experiment  defined 7 

Experimental  method 7 

Ferment 205 

Fermentation Y    '"';       .  '    ..        .    205 

Filtration .:._..      93 

Fire-damp .       ,       .,"     .        .        .182 

Flame 163 

of  the  argand  burner 167 

of  the  Bunsen's  burner 167 

of  the  candle .        .        .164 

of  the  gas-burner 167 

of  hydrogen 66 

tests  for  barium,  strontium,  and  calcium         ....    275 

tests  for  potassium  and  sodium 274 

Flowers  of  sulphur 102 

Fluorine 75 

Formulas,  of  compounds 40 

constitutional 56 

empirical 59 

graphic 56 

rational 59 

Fractional  distillation 185 

French  system  of  measures 21 

Fuel    .  .  ,162 


INDEX.  297 

Furnace,  the  blast .226 

the  cupola 227 

the  reverberatory 228 

Fusible  alloy 232 

Fusion  affecting  chemical  action 12 

Galena 203 

Gallium 222 

Gas,  illuminating 195 

from  petroleum 198 

Gases,  diffusion  of •.  128 

osmose  of 129 

liquefaction  of 64,  72,  84,  155 

solubility  of 91 

Gasoline 186 

Gay  Lussac's  Law 34 

German  silver 236 

Glass 144 

Glauber's  salts 81,  218 

Glucose 203 

Gold 243 

Graphic  formulas 56 

symbols 55 

Graphite 152 

Gravitation 10 

Gun-metal 236 

Heat  affecting  chemical  action 12 

Hydrates 47 

Hydrochloric  acid 76 

chemical  character  of 79 

composition  of 29 

molecular  weight  of 79 

preparation  of 77 

solubility  of 78 

uses  of 80 

Hypochlorous  acid 98 

Hydrogen 60 

as  a  standard 67 

chemical  properties  of 65 

combustibility  of 66 

combustion  of 88 

explosibility  of        .        ...        .        .        •        .        .67 

liquefaction  of 64 

molecular  formula  of 67 

occlusion  of     . 64 

occurrence  of 67 

physical  properties  of    .        .- 63 

preparation  of .        .  60. 61, 63 


INDEX. 


Hydrogen,  salts         ......        .        ....  46 

solubility  of    ........      .        .        .64 

units        ...........  67 

weight  of  one  liter  of    ........  67 

Hydrogen  arsenide   .....        ......  134 

Hydrogen  dioxide    ...........  96 

Hydrogen  nitride      ...........  117 

Hydrogen  phosphide        ..........  132 

Hydrogen  sulphide   .        .        .        ........  103 

Ice               .....        ........  89 

Illuminating  gas       ...........  195 

Indestructibility  of  matter      .........  17 

Indium       ........        .....  221 

Iodine         .............  75 

Iron     ...        ...........  224 

cast    .............  225 

casting      .........        ...  227 

compounds  of  ...........  276 

galvanized        .                .     %  .  ••   t  .    _  .       T       .        .        .        .  224 

malleable  .        .        .     \  .       ........  229 

ores  of       ............  225 

pig      .............  227 

puddling  ...........  229 

reduction  of  the  ores  of  .........  226 

wrought     .....        .......  229 

Isomeric  substances         ..........  205 

Isomerism  .        .        .        .    .    .    t    .    ^   .    ,   .        \        •        .    ^    .        .  209 

Kerosene    .......        ..._.-...        .186 

Law,  of  Avogadro    .        .        .        •     -  «       •       ».  .     •        «        •        .35 

of  constant  proportions       '  .     .   .  •  =  •  ,      .....  31 

of  Gay  Lussac          .        .        ........  34 

of  multiple  proportions          .        .        ......  31 

of  the  diffusion  of  gases     _..-..»       .        .        .        .        .  129 

Laws  of  combination       .        .        ........  29 

Lamp-black        ............  144 

Laughing-gas     ............  121 

Lead    .        ............  232 

action  of,  on  water  ..........  279 

compounds  of  ...........  278 

Light  ..............  165 

oxyhydrogen   ...........  168 

source  of  ............  168 

Lime  .........        .....  221 

Lime-water        ............  220 

Liquids,  diffusion  of         .........        .  127 

osmose  of    ...........  128 

Liquefaction  of  gases       ........  64,  72,  84,  155 


INDEX.  299 

Lake,  carmine *......  275 

Lakes 276 

Magnesium 223 

combustion  of 41 

Malachite   .        .        .        .                . 234 

Manganese 224 

Manufacture  of  illuminating  gas 195 

of  potassium  carbonate 217 

of  sodium  carbonate .  218 

of  sulphuric  acid 108 

Marsh-gas 182 

series 183 

Marsh's  test 135 

Measuring . ;        ...  21 

Mercuric  oxide 4 

decomposition  of 5 

Mercury 236 

Metallurgy 244 

Metals 54 

characteristic  properties  ot 214 

classification  of 215 

density  of 214 

melting-points  of 214 

symbols  of  the      .......        .        .        .        .        .215 

of  the  Alkalies     .        . 216 

of  the  Alkaline  earths 219 

of  the  Antimony  class *.  230 

of  the  Earths        . 221 

of  the  Gold  class 242 

of  the  Iron  class 224 

of  the  Lead  class 232 

of  the  Silver  class        . 233 

of  the  Tin  class 230 

of  the  Zinc  class 223 

Methane     .        .        .        . .183 

Methyl 183 

Methyl  alcohol 193 

Methyl  hydride          .                         183 

Metric  system 21 

Mineral  springs 92 

Mixture  defined 9 

Molecular  weights 35 

volumes 35 

Molecule  denned 34 

Molecules,  unsaturated    " 56 

Mortar 221 

Muriatic  acid     ....  80 


3  INDEX. 

Naphtha 186,199 

Nascent  state 117 

Nickel 224 

Nitric  acid 119 

an  oxidizing  agent 108,  120 

Nitric  anhydride 124 

Nitric  oxide 122 

Nitric  peroxide 123 

Nitro-benzol 200 

Nitrogen 115 

compound  with  hydrogen        .......    117 

compounds  with  oxygen 31,  119 

group  of  non-metals 138 

in  the  atmosphere 124 

occurrence  in  nature 117 

preparation  of 115 

properties  of      .        .        .        .        .        ,        *:      .        .  •     .    115 

Nitrous  anhydride 123 

Nitrous  oxide    .  .        .        ...        .        •        .        •        •    121 

Nomenclature 41 

of  acids 44 

of  binary  compounds 41 

of  hydrates 47 

of  oxides  .        .        .        .        .        .        .        .  .42 

of  salts 46 

Non-metals ,       v.  :"",.,<.        .        .      54 

classification  of    .        .        .        .        .        ._'.'•        .54 

The  Bivalent  group  .        .        .        ,.       ;        .       83, 112 

The  Trivalent  group  .        .        .       i        ,        .        .     115,138 
The  Univalent  group  .        .        .        ...        .        .        70, 75 

The  Quadrivalent  group 143,  146 

Notation 39 

Observation        .        .        .        .        ...        .        .  .        .        .        6 

Occlusion 64 

Oil  of  vitriol 109 

Olefiantgas 191 

Olefines 191 

Opal 143 

Ores 215 

Organic  chemistry 180 

Organic  substances 181 

Organized  bodies .     180 

Osmose  of  gases 129 

of  liquids     ....  *.    128 

Oxidation  in  combustion         .  160 

Oxides     .  .  ' 42 

Oxidizing  agent 108 


INDEX.  301 

Oxygen              83 

allotropic  form  of 87 

properties  of 84 

compounds  with  carbon 152 

compounds  with  chlorine 97 

compounds  with  hydrogen 88,  96,  99 

compounds  with  nitrogen         .......  119 

compounds  with  sulphur 105 

compound  with  silicon 143 

compounds  with  phosphorus 133 

group  of  non-metals 112 

in  the  atmosphere .        .  125 

liquefaction  of ~~  .  84 

occurrence  of      .        . 84 

preparation  of 83 

Oxyhydrogen  blow-pipe  .        .        .        .        .        .        .        .        .        .  170 

heat .        .  168 

light 168 

Oxysalts 46 

Ozone 86 

test-paper  for 262 

Paraffine 194 

Paraffines 184 

Pearlash     .        .        . 217 

Perissads 58 

Petroleum .        .  185 

decomposition  of 198 

origin  of 202 

Phosphorus        ....                130 

compounds  with  hydrogen 132 

compounds  with  oxygen 133 

phosphorescence  of 268 

uses  of 131 

Photography 240 

Photophone 112 

Pig-iron 227 

Platinum 244 

Potash 217 

Potassium  .............  216 

Precipitate 26,28 

Quantivalence 54 

Quicklime 221 

Safety-lamp 162 

Salt  in  sea-water 92 

Salt-cake 218 

Salts 45 

acid  .                                                             110 


302  INDEX. 

Salts,  haloid 46 

hydrogen 46 

names  of 46 

normal 110 

oxygen .46 

Scheele's  Green 269 

Selenium    . Ill 

Series,  the  alcohol 188 

the  ether 190 

the  marsh-gas 183 

homologous 191 

Silica 143 

Silicon 143 

Silver 237 

alloys  of 239 

compounds  of  affected  by  light 239 

Snowflakes 90 

Solution 11, 89 

Soda 219 

Soda-ash 219 

Soda-water 155 

Sodium 216 

acid  carbonate 219 

alum 223 

carbonate 218 

chloride 218 

sulphate ..."•*'.,..        .218 

sulphide .V.  *,-  :    .        .  218 

Specific  gravity .        .        .        .        .       .        .        ,        .  .        .38 

Spectrum  analysis    .        .        .      - 25 

Spirituous  liquors 205 

Starch 209 

Stalactites  and  stalagmites .        .  221 

Steel 229 

Sucrose 203 

Sugar 203 

varieties  of .        .203 

Sulphates 110 

Sulphur 101 

compound  with  hydrogen 103 

compounds  with  oxygen 105 

crystalline  forms 102 

occurrence  in  nature 103 

plastic 102 

uses  of 103 

Snlphurets 103 

Sulphuretted  hydrogen                            , 103 


INDEX.  303 

Sulphuric  acid  •. 108 

Sulphuric  ether 190 

Sulphurous  acid 106 

Sulphurous  oxide .        .        .       .    106 

Symbols 39 

Synthesis 23 

Tannic  acid,  test  for 278 

Tar 193,199 

Tellurium 112 

Thallium 232 

Tin 230 

Type-metal 231 

Unit,  of  combining  weights 31,  36 

of  quantivalence 55 

Units,  hydrogen 67 

Ventilation,  need  of 174 

Vinegar -      .        .    206 

Water 88 

action  of,  on  lead 233 

chalybeate 92 

combining  weight  of 32 

composition  of      . 99 

decomposition  of  .       .       .«>     . 5,7 

electrolysis 24 

freezing-point  of  .        .        ...       .        .        .        .        .89 

graphic  formula  of       .        .        .        ..•-..        .99 

hard  and  soft        .        .        ...       *        .        .        .        .      96 

in  the  atmosphere 125 

natural 92 

of  crystallization 138 

percentage  composition  of .25 

purification  of 93 

of  the  sea 92 

solvent  powers  of 89 

synthesis  of 26 

Water-gas 198 

Weighing .      20 

Weight,  a  measure  of  matter         .        .        .        .        •        •        •        .17 
Weights,  the  metric  system  of        ...        *-  ,  '.        •        •        .21 

Wood,  constituents  of .  *  ~     .        •        •        .201 

decay  of 174 

destructive  distillation  of 192 

tar 193 

vinegar  ....       . >^fgtJ-  *TraaaSSNC       *       '       '    ^ 
Wine ^^^'^^•^^Si       '        •    206 

zinc ^V   .OF.THI^CM^  •    ••  223 

malleability  oi  . 


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Chemicals  and  Utensils 

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